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#include <iostream>
#include <bits/stdc++.h>
using namespace std;
 
class Graph 
{ 
    int V;
 
    list<int> *adj; 
 
    void topologicalSortUtil(int v, bool visited[], stack<int> &Stack); 
public: 
    Graph(int V);
 
    void addEdge(int v, int w); 
 
    void topologicalSort(); 
}; 
 
Graph::Graph(int V) 
{ 
    this->V = V; 
    adj = new list<int>[V]; 
} 
 
void Graph::addEdge(int v, int w) 
{ 
    adj[v].push_back(w);
} 
 
void Graph::topologicalSortUtil(int v, bool visited[],  
                                stack<int> &Stack) 
{ 
 
    visited[v] = true; 
 
    list<int>::iterator i; 
    for (i = adj[v].begin(); i != adj[v].end(); ++i) 
        if (!visited[*i]) 
            topologicalSortUtil(*i, visited, Stack); 
 
    Stack.push(v); 
} 
 
string Graph::topologicalSort() 
{ 
    stack<int> Stack; 
  	string result;
    bool *visited = new bool[V]; 
    for (int i = 0; i < V; i++) 
        visited[i] = false; 
 
    for (int i = 0; i < V; i++) 
      if (visited[i] == false) 
        topologicalSortUtil(i, visited, Stack); 
 
    while (Stack.empty() == false) 
    { 
        result.append(Stack.top());
        Stack.pop(); 
    } 
    return String;
} 
 
int main() {
	int n,index;
	bool res=true;
	cin>>n;
	vector<string> arr;
	cin.ignore(numeric_limits::max(),'\n');
 
	for(int i=0;i<n;i++)
		cin.getline(arr[i]);
 
	Graph* g = new Graph(26);
 
	for(int i=0;i<n-1;i++){
		index1=index2=0;
 
		while(arr[i][index]!='\0' && arr[i+1][index]!='\0' && arr[i][index1]==arr[i+1][index2])
			index++;
 
		if(arr[i][index]=='\0' || arr[i+1][index]=='\0'){
			res=false;
			break;
		}
 
		else{
			g->addEdge(arr[i][index]-'a',arr[i+1][index]-'a');
		}
 
	}
 
	cout<<g->topologicalSort();
 
	return 0;
}

prog.cpp:45:8: error: no declaration matches ‘std::__cxx11::string Graph::topologicalSort()’
 string Graph::topologicalSort()
        ^~~~~
prog.cpp:17:10: note: candidate is: ‘void Graph::topologicalSort()’
     void topologicalSort();
          ^~~~~~~~~~~~~~~
prog.cpp:5:7: note: ‘class Graph’ defined here
 class Graph
       ^~~~~
prog.cpp: In function ‘int main()’:
prog.cpp:70:13: error: ‘template<class _Tp> struct std::numeric_limits’ used without template parameters
  cin.ignore(numeric_limits::max(),'\n');
             ^~~~~~~~~~~~~~
prog.cpp:73:21: error: no matching function for call to ‘std::basic_istream<char>::getline(__gnu_cxx::__alloc_traits<std::allocator<std::__cxx11::basic_string<char> >, std::__cxx11::basic_string<char> >::value_type&)’
   cin.getline(arr[i]);
                     ^
In file included from /usr/include/c++/8/iostream:40,
                 from prog.cpp:1:
/usr/include/c++/8/istream:647:5: note: candidate: ‘std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::getline(std::basic_istream<_CharT, _Traits>::char_type*, std::streamsize, std::basic_istream<_CharT, _Traits>::char_type) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::char_type = char; std::streamsize = long int]’
     basic_istream<char>::
     ^~~~~~~~~~~~~~~~~~~
/usr/include/c++/8/istream:647:5: note:   candidate expects 3 arguments, 1 provided
/usr/include/c++/8/istream:427:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::getline(std::basic_istream<_CharT, _Traits>::char_type*, std::streamsize) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>; std::basic_istream<_CharT, _Traits>::char_type = char; std::streamsize = long int]’
       getline(char_type* __s, streamsize __n)
       ^~~~~~~
/usr/include/c++/8/istream:427:7: note:   candidate expects 2 arguments, 1 provided
prog.cpp:78:3: error: ‘index1’ was not declared in this scope
   index1=index2=0;
   ^~~~~~
prog.cpp:78:3: note: suggested alternative: ‘index’
   index1=index2=0;
   ^~~~~~
   index
prog.cpp:78:10: error: ‘index2’ was not declared in this scope
   index1=index2=0;
          ^~~~~~
prog.cpp:78:10: note: suggested alternative: ‘index’
   index1=index2=0;
          ^~~~~~
          index
prog.cpp:94:6: error: no match for ‘operator<<’ (operand types are ‘std::ostream’ {aka ‘std::basic_ostream<char>’} and ‘void’)
  cout<<g->topologicalSort();
  ~~~~^~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/8/iostream:39,
                 from prog.cpp:1:
/usr/include/c++/8/ostream:108:7: note: candidate: ‘std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__ostream_type& (*)(std::basic_ostream<_CharT, _Traits>::__ostream_type&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]’
       operator<<(__ostream_type& (*__pf)(__ostream_type&))
       ^~~~~~~~
/usr/include/c++/8/ostream:108:7: note:   no known conversion for argument 1 from ‘void’ to ‘std::basic_ostream<char>::__ostream_type& (*)(std::basic_ostream<char>::__ostream_type&)’ {aka ‘std::basic_ostream<char>& (*)(std::basic_ostream<char>&)’}
/usr/include/c++/8/ostream:117:7: note: candidate: ‘std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__ios_type& (*)(std::basic_ostream<_CharT, _Traits>::__ios_type&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>; std::basic_ostream<_CharT, _Traits>::__ios_type = std::basic_ios<char>]’
       operator<<(__ios_type& (*__pf)(__ios_type&))
       ^~~~~~~~
/usr/include/c++/8/ostream:117:7: note:   no known conversion for argument 1 from ‘void’ to ‘std::basic_ostream<char>::__ios_type& (*)(std::basic_ostream<char>::__ios_type&)’ {aka ‘std::basic_ios<char>& (*)(std::basic_ios<char>&)’}
/usr/include/c++/8/ostream:127:7: note: candidate: ‘std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::ios_base& (*)(std::ios_base&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]’
       operator<<(ios_base& (*__pf) (ios_base&))
       ^~~~~~~~
/usr/include/c++/8/ostream:127:7: note:   no known conversion for argument 1 from ‘void’ to ‘std::ios_base& (*)(std::ios_base&)’
/usr/include/c++/8/ostream:166:7: note: candidate: ‘std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long int) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]’
       operator<<(long __n)
       ^~~~~~~~
/usr/include/c++/8/ostream:166:7: note:   no known conversion for argument 1 from ‘void’ to ‘long int’
/usr/include/c++/8/ostream:170:7: note: candidate: ‘std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long unsigned int) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]’
       operator<<(unsigned long __n)
       ^~~~~~~~
/usr/include/c++/8/ostream:170:7: note:   no known conversion for argument 1 from ‘void’ to ‘long unsigned int’
/usr/include/c++/8/ostream:174:7: note: candidate: ‘std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(bool) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]’
       operator<<(bool __n)
       ^~~~~~~~
/usr/include/c++/8/ostream:174:7: note:   no known conversion for argument 1 from ‘void’ to ‘bool’
In file included from /usr/include/c++/8/ostream:693,
                 from /usr/include/c++/8/iostream:39,
                 from prog.cpp:1:
/usr/include/c++/8/bits/ostream.tcc:91:5: note: candidate: ‘std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(short int) [with _CharT = char; _Traits = std::char_traits<char>]’
     basic_ostream<_CharT, _Traits>::
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/8/bits/ostream.tcc:91:5: note:   no known conversion for argument 1 from ‘void’ to ‘short int’
In file included from /usr/include/c++/8/iostream:39,
                 from prog.cpp:1:
/usr/include/c++/8/ostream:181:7: note: candidate: ‘std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(short unsigned int) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]’
       operator<<(unsigned short __n)
       ^~~~~~~~
/usr/include/c++/8/ostream:181:7: note:   no known conversion for argument 1 from ‘void’ to ‘short unsigned int’
In file included from /usr/include/c++/8/ostream:693,
                 from /usr/include/c++/8/iostream:39,
                 from prog.cpp:1:
/usr/include/c++/8/bits/ostream.tcc:105:5: note: candidate: ‘std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(int) [with _CharT = char; _Traits = std::char_traits<char>]’
     basic_ostream<_CharT, _Traits>::
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/8/bits/ostream.tcc:105:5: note:   no known conversion for argument 1 from ‘void’ to ‘int’
In file included from /usr/include/c++/8/iostream:39,
                 from prog.cpp:1:
/usr/include/c++/8/ostream:192:7: note: candidate: ‘std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(unsigned int) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]’
       operator<<(unsigned int __n)
       ^~~~~~~~
/usr/include/c++/8/ostream:192:7: note:   no known conversion for argument 1 from ‘void’ to ‘unsigned int’
/usr/include/c++/8/ostream:201:7: note: candidate: ‘std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long long int) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]’
       operator<<(long long __n)
       ^~~~~~~~
/usr/include/c++/8/ostream:201:7: note:   no known conversion for argument 1 from ‘void’ to ‘long long int’
/usr/include/c++/8/ostream:205:7: note: candidate: ‘std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long long unsigned int) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]’
       operator<<(unsigned long long __n)
       ^~~~~~~~
/usr/include/c++/8/ostream:205:7: note:   no known conversion for argument 1 from ‘void’ to ‘long long unsigned int’
/usr/include/c++/8/ostream:220:7: note: candidate: ‘std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(double) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]’
       operator<<(double __f)
       ^~~~~~~~
/usr/include/c++/8/ostream:220:7: note:   no known conversion for argument 1 from ‘void’ to ‘double’
/usr/include/c++/8/ostream:224:7: note: candidate: ‘std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(float) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]’
       operator<<(float __f)
       ^~~~~~~~
/usr/include/c++/8/ostream:224:7: note:   no known conversion for argument 1 from ‘void’ to ‘float’
/usr/include/c++/8/ostream:232:7: note: candidate: ‘std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long double) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]’
       operator<<(long double __f)
       ^~~~~~~~
/usr/include/c++/8/ostream:232:7: note:   no known conversion for argument 1 from ‘void’ to ‘long double’
/usr/include/c++/8/ostream:245:7: note: candidate: ‘std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(const void*) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]’
       operator<<(const void* __p)
       ^~~~~~~~
/usr/include/c++/8/ostream:245:7: note:   no known conversion for argument 1 from ‘void’ to ‘const void*’
In file included from /usr/include/c++/8/ostream:693,
                 from /usr/include/c++/8/iostream:39,
                 from prog.cpp:1:
/usr/include/c++/8/bits/ostream.tcc:119:5: note: candidate: ‘std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__streambuf_type*) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__streambuf_type = std::basic_streambuf<char>]’
     basic_ostream<_CharT, _Traits>::
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/8/bits/ostream.tcc:119:5: note:   no known conversion for argument 1 from ‘void’ to ‘std::basic_ostream<char>::__streambuf_type*’ {aka ‘std::basic_streambuf<char>*’}
In file included from /usr/include/c++/8/regex:62,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:110,
                 from prog.cpp:2:
/usr/include/c++/8/bits/regex.h:1523:5: note: candidate: ‘template<class _Ch_type, class _Ch_traits, class _Bi_iter> std::basic_ostream<_CharT, _Traits>& std::__cxx11::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::__cxx11::sub_match<_Bi_iter>&)’
     operator<<(basic_ostream<_Ch_type, _Ch_traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/regex.h:1523:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::__cxx11::sub_match<_Bi_iter>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/string:52,
                 from /usr/include/c++/8/bits/locale_classes.h:40,
                 from /usr/include/c++/8/bits/ios_base.h:41,
                 from /usr/include/c++/8/ios:42,
                 from /usr/include/c++/8/ostream:38,
                 from /usr/include/c++/8/iostream:39,
                 from prog.cpp:1:
/usr/include/c++/8/bits/basic_string.h:6323:5: note: candidate: ‘template<class _CharT, class _Traits, class _Alloc> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&)’
     operator<<(basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/basic_string.h:6323:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/bits/ios_base.h:46,
                 from /usr/include/c++/8/ios:42,
                 from /usr/include/c++/8/ostream:38,
                 from /usr/include/c++/8/iostream:39,
                 from prog.cpp:1:
/usr/include/c++/8/system_error:217:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::error_code&)’
     operator<<(basic_ostream<_CharT, _Traits>& __os, const error_code& __e)
     ^~~~~~~~
/usr/include/c++/8/system_error:217:5: note:   template argument deduction/substitution failed:
prog.cpp:94:26: note:   cannot convert ‘g->Graph::topologicalSort()’ (type ‘void’) to type ‘const std::error_code&’
  cout<<g->topologicalSort();
        ~~~~~~~~~~~~~~~~~~^~
In file included from /usr/include/c++/8/iostream:39,
                 from prog.cpp:1:
/usr/include/c++/8/ostream:497:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, _CharT)’
     operator<<(basic_ostream<_CharT, _Traits>& __out, _CharT __c)
     ^~~~~~~~
/usr/include/c++/8/ostream:497:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   deduced conflicting types for parameter ‘_CharT’ (‘char’ and ‘void’)
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/iostream:39,
                 from prog.cpp:1:
/usr/include/c++/8/ostream:502:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, char)’
     operator<<(basic_ostream<_CharT, _Traits>& __out, char __c)
     ^~~~~~~~
/usr/include/c++/8/ostream:502:5: note:   template argument deduction/substitution failed:
prog.cpp:94:26: note:   cannot convert ‘g->Graph::topologicalSort()’ (type ‘void’) to type ‘char’
  cout<<g->topologicalSort();
        ~~~~~~~~~~~~~~~~~~^~
In file included from /usr/include/c++/8/iostream:39,
                 from prog.cpp:1:
/usr/include/c++/8/ostream:508:5: note: candidate: ‘template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, char)’
     operator<<(basic_ostream<char, _Traits>& __out, char __c)
     ^~~~~~~~
/usr/include/c++/8/ostream:508:5: note:   template argument deduction/substitution failed:
prog.cpp:94:26: note:   cannot convert ‘g->Graph::topologicalSort()’ (type ‘void’) to type ‘char’
  cout<<g->topologicalSort();
        ~~~~~~~~~~~~~~~~~~^~
In file included from /usr/include/c++/8/iostream:39,
                 from prog.cpp:1:
/usr/include/c++/8/ostream:514:5: note: candidate: ‘template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, signed char)’
     operator<<(basic_ostream<char, _Traits>& __out, signed char __c)
     ^~~~~~~~
/usr/include/c++/8/ostream:514:5: note:   template argument deduction/substitution failed:
prog.cpp:94:26: note:   cannot convert ‘g->Graph::topologicalSort()’ (type ‘void’) to type ‘signed char’
  cout<<g->topologicalSort();
        ~~~~~~~~~~~~~~~~~~^~
In file included from /usr/include/c++/8/iostream:39,
                 from prog.cpp:1:
/usr/include/c++/8/ostream:519:5: note: candidate: ‘template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, unsigned char)’
     operator<<(basic_ostream<char, _Traits>& __out, unsigned char __c)
     ^~~~~~~~
/usr/include/c++/8/ostream:519:5: note:   template argument deduction/substitution failed:
prog.cpp:94:26: note:   cannot convert ‘g->Graph::topologicalSort()’ (type ‘void’) to type ‘unsigned char’
  cout<<g->topologicalSort();
        ~~~~~~~~~~~~~~~~~~^~
In file included from /usr/include/c++/8/iostream:39,
                 from prog.cpp:1:
/usr/include/c++/8/ostream:539:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const _CharT*)’
     operator<<(basic_ostream<_CharT, _Traits>& __out, const _CharT* __s)
     ^~~~~~~~
/usr/include/c++/8/ostream:539:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const _CharT*’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/ostream:693,
                 from /usr/include/c++/8/iostream:39,
                 from prog.cpp:1:
/usr/include/c++/8/bits/ostream.tcc:321:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const char*)’
     operator<<(basic_ostream<_CharT, _Traits>& __out, const char* __s)
     ^~~~~~~~
/usr/include/c++/8/bits/ostream.tcc:321:5: note:   template argument deduction/substitution failed:
prog.cpp:94:26: note:   cannot convert ‘g->Graph::topologicalSort()’ (type ‘void’) to type ‘const char*’
  cout<<g->topologicalSort();
        ~~~~~~~~~~~~~~~~~~^~
In file included from /usr/include/c++/8/iostream:39,
                 from prog.cpp:1:
/usr/include/c++/8/ostream:556:5: note: candidate: ‘template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, const char*)’
     operator<<(basic_ostream<char, _Traits>& __out, const char* __s)
     ^~~~~~~~
/usr/include/c++/8/ostream:556:5: note:   template argument deduction/substitution failed:
prog.cpp:94:26: note:   cannot convert ‘g->Graph::topologicalSort()’ (type ‘void’) to type ‘const char*’
  cout<<g->topologicalSort();
        ~~~~~~~~~~~~~~~~~~^~
In file included from /usr/include/c++/8/iostream:39,
                 from prog.cpp:1:
/usr/include/c++/8/ostream:569:5: note: candidate: ‘template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, const signed char*)’
     operator<<(basic_ostream<char, _Traits>& __out, const signed char* __s)
     ^~~~~~~~
/usr/include/c++/8/ostream:569:5: note:   template argument deduction/substitution failed:
prog.cpp:94:26: note:   cannot convert ‘g->Graph::topologicalSort()’ (type ‘void’) to type ‘const signed char*’
  cout<<g->topologicalSort();
        ~~~~~~~~~~~~~~~~~~^~
In file included from /usr/include/c++/8/iostream:39,
                 from prog.cpp:1:
/usr/include/c++/8/ostream:574:5: note: candidate: ‘template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, const unsigned char*)’
     operator<<(basic_ostream<char, _Traits>& __out, const unsigned char* __s)
     ^~~~~~~~
/usr/include/c++/8/ostream:574:5: note:   template argument deduction/substitution failed:
prog.cpp:94:26: note:   cannot convert ‘g->Graph::topologicalSort()’ (type ‘void’) to type ‘const unsigned char*’
  cout<<g->topologicalSort();
        ~~~~~~~~~~~~~~~~~~^~
In file included from /usr/include/c++/8/iostream:39,
                 from prog.cpp:1:
/usr/include/c++/8/ostream:682:5: note: candidate: ‘template<class _Ostream, class _Tp> typename std::enable_if<std::__and_<std::__not_<std::is_lvalue_reference<_Tp> >, std::__is_convertible_to_basic_ostream<_Ostream>, std::__is_insertable<typename std::__is_convertible_to_basic_ostream<_Tp>::__ostream_type, const _Tp&, void> >::value, typename std::__is_convertible_to_basic_ostream<_Tp>::__ostream_type>::type std::operator<<(_Ostream&&, const _Tp&)’
     operator<<(_Ostream&& __os, const _Tp& __x)
     ^~~~~~~~
/usr/include/c++/8/ostream:682:5: note:   template argument deduction/substitution failed:
/usr/include/c++/8/ostream: In substitution of ‘template<class _Ostream, class _Tp> typename std::enable_if<std::__and_<std::__not_<std::is_lvalue_reference<_Tp> >, std::__is_convertible_to_basic_ostream<_Ostream>, std::__is_insertable<typename std::__is_convertible_to_basic_ostream<_Tp>::__ostream_type, const _Tp&, void> >::value, typename std::__is_convertible_to_basic_ostream<_Tp>::__ostream_type>::type std::operator<<(_Ostream&&, const _Tp&) [with _Ostream = std::basic_ostream<char>&; _Tp = void]’:
prog.cpp:94:27:   required from here
/usr/include/c++/8/ostream:682:5: error: forming reference to void
In file included from /usr/include/c++/8/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:52,
                 from prog.cpp:2:
/usr/include/c++/8/complex:547:5: note: candidate: ‘template<class _Tp, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::complex<_Tp>&)’
     operator<<(basic_ostream<_CharT, _Traits>& __os, const complex<_Tp>& __x)
     ^~~~~~~~
/usr/include/c++/8/complex:547:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::complex<_Tp>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:66,
                 from prog.cpp:2:
/usr/include/c++/8/bitset:1534:5: note: candidate: ‘template<class _CharT, class _Traits, long unsigned int _Nb> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::bitset<_Nb>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bitset:1534:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::bitset<_Nb>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:72,
                 from prog.cpp:2:
/usr/include/c++/8/iomanip:79:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, std::_Resetiosflags)’
     operator<<(basic_ostream<_CharT, _Traits>& __os, _Resetiosflags __f)
     ^~~~~~~~
/usr/include/c++/8/iomanip:79:5: note:   template argument deduction/substitution failed:
prog.cpp:94:26: note:   cannot convert ‘g->Graph::topologicalSort()’ (type ‘void’) to type ‘std::_Resetiosflags’
  cout<<g->topologicalSort();
        ~~~~~~~~~~~~~~~~~~^~
In file included from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:72,
                 from prog.cpp:2:
/usr/include/c++/8/iomanip:109:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, std::_Setiosflags)’
     operator<<(basic_ostream<_CharT, _Traits>& __os, _Setiosflags __f)
     ^~~~~~~~
/usr/include/c++/8/iomanip:109:5: note:   template argument deduction/substitution failed:
prog.cpp:94:26: note:   cannot convert ‘g->Graph::topologicalSort()’ (type ‘void’) to type ‘std::_Setiosflags’
  cout<<g->topologicalSort();
        ~~~~~~~~~~~~~~~~~~^~
In file included from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:72,
                 from prog.cpp:2:
/usr/include/c++/8/iomanip:143:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, std::_Setbase)’
     operator<<(basic_ostream<_CharT, _Traits>& __os, _Setbase __f)
     ^~~~~~~~
/usr/include/c++/8/iomanip:143:5: note:   template argument deduction/substitution failed:
prog.cpp:94:26: note:   cannot convert ‘g->Graph::topologicalSort()’ (type ‘void’) to type ‘std::_Setbase’
  cout<<g->topologicalSort();
        ~~~~~~~~~~~~~~~~~~^~
In file included from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:72,
                 from prog.cpp:2:
/usr/include/c++/8/iomanip:178:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, std::_Setfill<_CharT>)’
     operator<<(basic_ostream<_CharT, _Traits>& __os, _Setfill<_CharT> __f)
     ^~~~~~~~
/usr/include/c++/8/iomanip:178:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘std::_Setfill<_CharT>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:72,
                 from prog.cpp:2:
/usr/include/c++/8/iomanip:208:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, std::_Setprecision)’
     operator<<(basic_ostream<_CharT, _Traits>& __os, _Setprecision __f)
     ^~~~~~~~
/usr/include/c++/8/iomanip:208:5: note:   template argument deduction/substitution failed:
prog.cpp:94:26: note:   cannot convert ‘g->Graph::topologicalSort()’ (type ‘void’) to type ‘std::_Setprecision’
  cout<<g->topologicalSort();
        ~~~~~~~~~~~~~~~~~~^~
In file included from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:72,
                 from prog.cpp:2:
/usr/include/c++/8/iomanip:238:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, std::_Setw)’
     operator<<(basic_ostream<_CharT, _Traits>& __os, _Setw __f)
     ^~~~~~~~
/usr/include/c++/8/iomanip:238:5: note:   template argument deduction/substitution failed:
prog.cpp:94:26: note:   cannot convert ‘g->Graph::topologicalSort()’ (type ‘void’) to type ‘std::_Setw’
  cout<<g->topologicalSort();
        ~~~~~~~~~~~~~~~~~~^~
In file included from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:72,
                 from prog.cpp:2:
/usr/include/c++/8/iomanip:311:5: note: candidate: ‘template<class _CharT, class _Traits, class _MoneyT> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, std::_Put_money<_MoneyT>)’
     operator<<(basic_ostream<_CharT, _Traits>& __os, _Put_money<_MoneyT> __f)
     ^~~~~~~~
/usr/include/c++/8/iomanip:311:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘std::_Put_money<_MoneyT>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:72,
                 from prog.cpp:2:
/usr/include/c++/8/iomanip:363:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, std::_Put_time<_CharT>)’
     operator<<(basic_ostream<_CharT, _Traits>& __os, _Put_time<_CharT> __f)
     ^~~~~~~~
/usr/include/c++/8/iomanip:363:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘std::_Put_time<_CharT>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/memory:81,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:82,
                 from prog.cpp:2:
/usr/include/c++/8/bits/shared_ptr.h:66:5: note: candidate: ‘template<class _Ch, class _Tr, class _Tp, __gnu_cxx::_Lock_policy _Lp> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::__shared_ptr<_Tp, _Lp>&)’
     operator<<(std::basic_ostream<_Ch, _Tr>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/shared_ptr.h:66:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::__shared_ptr<_Tp, _Lp>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/valarray:592,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:95,
                 from prog.cpp:2:
/usr/include/c++/8/bits/valarray_after.h:410:5: note: candidate: ‘template<class _Dom1, class _Dom2> std::_Expr<std::_BinClos<std::__shift_left, std::_Expr, std::_Expr, _Dom1, _Dom2>, typename std::__fun<std::__shift_left, typename _Dom1::value_type>::result_type> std::operator<<(const std::_Expr<_Dom1, typename _Dom1::value_type>&, const std::_Expr<_Dom2, typename _Dom2::value_type>&)’
     _DEFINE_EXPR_BINARY_OPERATOR(<<, __shift_left)
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/8/bits/valarray_after.h:410:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   ‘std::ostream’ {aka ‘std::basic_ostream<char>’} is not derived from ‘const std::_Expr<_Dom1, typename _Dom1::value_type>’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/valarray:592,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:95,
                 from prog.cpp:2:
/usr/include/c++/8/bits/valarray_after.h:410:5: note: candidate: ‘template<class _Dom> std::_Expr<std::_BinClos<std::__shift_left, std::_Expr, std::_Constant, _Dom, typename _Dom::value_type>, typename std::__fun<std::__shift_left, typename _Dom1::value_type>::result_type> std::operator<<(const std::_Expr<_Dom1, typename _Dom1::value_type>&, const typename _Dom::value_type&)’
     _DEFINE_EXPR_BINARY_OPERATOR(<<, __shift_left)
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/8/bits/valarray_after.h:410:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   ‘std::ostream’ {aka ‘std::basic_ostream<char>’} is not derived from ‘const std::_Expr<_Dom1, typename _Dom1::value_type>’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/valarray:592,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:95,
                 from prog.cpp:2:
/usr/include/c++/8/bits/valarray_after.h:410:5: note: candidate: ‘template<class _Dom> std::_Expr<std::_BinClos<std::__shift_left, std::_Constant, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__shift_left, typename _Dom1::value_type>::result_type> std::operator<<(const typename _Dom::value_type&, const std::_Expr<_Dom1, typename _Dom1::value_type>&)’
     _DEFINE_EXPR_BINARY_OPERATOR(<<, __shift_left)
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/8/bits/valarray_after.h:410:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::_Expr<_Dom1, typename _Dom1::value_type>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/valarray:592,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:95,
                 from prog.cpp:2:
/usr/include/c++/8/bits/valarray_after.h:410:5: note: candidate: ‘template<class _Dom> std::_Expr<std::_BinClos<std::__shift_left, std::_Expr, std::_ValArray, _Dom, typename _Dom::value_type>, typename std::__fun<std::__shift_left, typename _Dom1::value_type>::result_type> std::operator<<(const std::_Expr<_Dom1, typename _Dom1::value_type>&, const std::valarray<typename _Dom::value_type>&)’
     _DEFINE_EXPR_BINARY_OPERATOR(<<, __shift_left)
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/8/bits/valarray_after.h:410:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   ‘std::ostream’ {aka ‘std::basic_ostream<char>’} is not derived from ‘const std::_Expr<_Dom1, typename _Dom1::value_type>’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/valarray:592,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:95,
                 from prog.cpp:2:
/usr/include/c++/8/bits/valarray_after.h:410:5: note: candidate: ‘template<class _Dom> std::_Expr<std::_BinClos<std::__shift_left, std::_ValArray, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__shift_left, typename _Dom1::value_type>::result_type> std::operator<<(const std::valarray<typename _Dom::value_type>&, const std::_Expr<_Dom1, typename _Dom1::value_type>&)’
     _DEFINE_EXPR_BINARY_OPERATOR(<<, __shift_left)
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/8/bits/valarray_after.h:410:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::_Expr<_Dom1, typename _Dom1::value_type>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:95,
                 from prog.cpp:2:
/usr/include/c++/8/valarray:1180:1: note: candidate: ‘template<class _Tp> std::_Expr<std::_BinClos<std::__shift_left, std::_ValArray, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__shift_left, _Tp>::result_type> std::operator<<(const std::valarray<_Tp>&, const std::valarray<_Tp>&)’
 _DEFINE_BINARY_OPERATOR(<<, __shift_left)
 ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/8/valarray:1180:1: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   ‘std::ostream’ {aka ‘std::basic_ostream<char>’} is not derived from ‘const std::valarray<_Tp>’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:95,
                 from prog.cpp:2:
/usr/include/c++/8/valarray:1180:1: note: candidate: ‘template<class _Tp> std::_Expr<std::_BinClos<std::__shift_left, std::_ValArray, std::_Constant, _Tp, _Tp>, typename std::__fun<std::__shift_left, _Tp>::result_type> std::operator<<(const std::valarray<_Tp>&, const _Tp&)’
 _DEFINE_BINARY_OPERATOR(<<, __shift_left)
 ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/8/valarray:1180:1: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   ‘std::ostream’ {aka ‘std::basic_ostream<char>’} is not derived from ‘const std::valarray<_Tp>’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:95,
                 from prog.cpp:2:
/usr/include/c++/8/valarray:1180:1: note: candidate: ‘template<class _Tp> std::_Expr<std::_BinClos<std::__shift_left, std::_Constant, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__shift_left, _Tp>::result_type> std::operator<<(const _Tp&, const std::valarray<_Tp>&)’
 _DEFINE_BINARY_OPERATOR(<<, __shift_left)
 ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/8/valarray:1180:1: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::valarray<_Tp>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/future:39,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:105,
                 from prog.cpp:2:
/usr/include/c++/8/thread:323:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, std::thread::id)’
     operator<<(basic_ostream<_CharT, _Traits>& __out, thread::id __id)
     ^~~~~~~~
/usr/include/c++/8/thread:323:5: note:   template argument deduction/substitution failed:
prog.cpp:94:26: note:   cannot convert ‘g->Graph::topologicalSort()’ (type ‘void’) to type ‘std::thread::id’
  cout<<g->topologicalSort();
        ~~~~~~~~~~~~~~~~~~^~
In file included from /usr/include/c++/8/random:49,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.h:1262:5: note: candidate: ‘template<class _RandomNumberEngine, long unsigned int __w, class _UIntType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::independent_bits_engine<_RandomNumberEngine, __w, _UIntType>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.h:1262:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::independent_bits_engine<_RandomNumberEngine, __w, _UIntType>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:874:5: note: candidate: ‘template<class _IntType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::uniform_int_distribution<_IntType>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:874:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::uniform_int_distribution<_IntType>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:933:5: note: candidate: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::uniform_real_distribution<_IntType>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:933:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::uniform_real_distribution<_IntType>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:2126:5: note: candidate: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::cauchy_distribution<_RealType>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:2126:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::cauchy_distribution<_RealType>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:995:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::bernoulli_distribution&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:995:5: note:   template argument deduction/substitution failed:
prog.cpp:94:26: note:   cannot convert ‘g->Graph::topologicalSort()’ (type ‘void’) to type ‘const std::bernoulli_distribution&’
  cout<<g->topologicalSort();
        ~~~~~~~~~~~~~~~~~~^~
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:1077:5: note: candidate: ‘template<class _IntType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::geometric_distribution<_IntType>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:1077:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::geometric_distribution<_IntType>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:1734:5: note: candidate: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::exponential_distribution<_RealType>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:1734:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::exponential_distribution<_RealType>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:2525:5: note: candidate: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::weibull_distribution<_RealType>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:2525:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::weibull_distribution<_RealType>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:2601:5: note: candidate: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::extreme_value_distribution<_RealType>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:2601:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::extreme_value_distribution<_RealType>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:153:5: note: candidate: ‘template<class _UIntType, _UIntType __a, _UIntType __c, _UIntType __m, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::linear_congruential_engine<_UIntType, __a, __c, __m>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:153:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::linear_congruential_engine<_UIntType, __a, __c, __m>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:474:5: note: candidate: ‘template<class _UIntType1, long unsigned int __w1, long unsigned int __n1, long unsigned int __m1, long unsigned int __r1, _UIntType1 __a1, long unsigned int __u1, _UIntType1 __d1, long unsigned int __s1, _UIntType1 __b1, long unsigned int __t1, _UIntType1 __c1, long unsigned int __l1, _UIntType1 __f1, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::mersenne_twister_engine<_UIntType, __w, __n, __m, __r, __a, __u, __d, __s, __b, __t, __c, __l, __f>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:474:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::mersenne_twister_engine<_UIntType, __w, __n, __m, __r, __a, __u, __d, __s, __b, __t, __c, __l, __f>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:629:5: note: candidate: ‘template<class _UIntType, long unsigned int __w, long unsigned int __s, long unsigned int __r, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::subtract_with_carry_engine<_UIntType, __w, __s, __r>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:629:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::subtract_with_carry_engine<_UIntType, __w, __s, __r>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:699:5: note: candidate: ‘template<class _RandomNumberEngine, long unsigned int __p, long unsigned int __r, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::discard_block_engine<_RandomNumberEngine, __p, __r>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:699:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::discard_block_engine<_RandomNumberEngine, __p, __r>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:828:5: note: candidate: ‘template<class _RandomNumberEngine, long unsigned int __k, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::shuffle_order_engine<_RandomNumberEngine, __k>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:828:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::shuffle_order_engine<_RandomNumberEngine, __k>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:1192:5: note: candidate: ‘template<class _IntType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::negative_binomial_distribution<_IntType>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:1192:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::negative_binomial_distribution<_IntType>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:1403:5: note: candidate: ‘template<class _IntType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::poisson_distribution<_IntType>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:1403:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::poisson_distribution<_IntType>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:1670:5: note: candidate: ‘template<class _IntType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::binomial_distribution<_IntType>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:1670:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::binomial_distribution<_IntType>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:1901:5: note: candidate: ‘template<class _RealType1, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::normal_distribution<_RealType>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:1901:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::normal_distribution<_RealType>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:1966:5: note: candidate: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::lognormal_distribution<_RealType>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:1966:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::lognormal_distribution<_RealType>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:2039:5: note: candidate: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::chi_squared_distribution<_RealType>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:2039:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::chi_squared_distribution<_RealType>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:2203:5: note: candidate: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::fisher_f_distribution<_RealType>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:2203:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::fisher_f_distribution<_RealType>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:2278:5: note: candidate: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::student_t_distribution<_RealType>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:2278:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::student_t_distribution<_RealType>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:2447:5: note: candidate: ‘template<class _RealType1, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::gamma_distribution<_RealType>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:2447:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::gamma_distribution<_RealType>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:2737:5: note: candidate: ‘template<class _IntType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::discrete_distribution<_IntType>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:2737:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::discrete_distribution<_IntType>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:2947:5: note: candidate: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::piecewise_constant_distribution<_RealType>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:2947:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::piecewise_constant_distribution<_RealType>’ and ‘void’
  cout<<g->topologicalSort();
                           ^
In file included from /usr/include/c++/8/random:51,
                 from /usr/include/x86_64-linux-gnu/c++/8/bits/stdc++.h:108,
                 from prog.cpp:2:
/usr/include/c++/8/bits/random.tcc:3163:5: note: candidate: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::piecewise_linear_distribution<_RealType>&)’
     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
     ^~~~~~~~
/usr/include/c++/8/bits/random.tcc:3163:5: note:   template argument deduction/substitution failed:
prog.cpp:94:27: note:   mismatched types ‘const std::piecewise_linear_distribution<_RealType>’ and ‘void’
  cout<<g->topologicalSort();
                           ^

Standard output is empty