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  1. //http://stackoverflow.com/questions/3780994/string-reversal-in-c
  2.  
  3. #include <iostream>
  4. #include <algorithm>
  5. #include <vector>
  6. #include <string>
  7. #include <sstream>
  8. using namespace std;
  9.  
  10. string test_string = " This   is my test    string";
  11.  
  12. int main() {
  13.     typedef pair <string::size_type,string::size_type> word_boundaries;
  14.     typedef vector <word_boundaries> word_boundaries_vector;
  15.     word_boundaries_vector words, spaces;
  16.  
  17. 	bool first_is_char = test_string[0] != ' ';
  18.  
  19.     for(string::size_type pos=0; pos != string::npos;) {
  20.         bool is_char = test_string[pos] != ' ';
  21.         string::size_type pos_end_token = string::npos;
  22.  
  23.         if (is_char)
  24.             pos_end_token = test_string.find(' ', pos);
  25.         else
  26.             pos_end_token = test_string.find_first_not_of(' ',pos);
  27.  
  28.         //word_boundaries token = make_pair(pos,pos_end_token == string::npos ? string::npos : pos_end_token-pos);
  29.         word_boundaries token;
  30.         token.first = pos;
  31.         token.second = pos_end_token == string::npos ? string::npos : pos_end_token-pos;
  32.  
  33.         if (is_char)
  34.             words.push_back(token);
  35.         else
  36.             spaces.push_back(token);
  37.  
  38.         pos = pos_end_token;
  39.     }
  40.  
  41.     stringstream ss;
  42.  
  43.     word_boundaries_vector::const_reverse_iterator it_w = words.rbegin();
  44.     word_boundaries_vector::const_iterator it_s = spaces.begin();
  45.  
  46.     word_boundaries b;
  47.  
  48. 	if (!first_is_char)
  49. 	{
  50.         b = *it_s++;
  51. 		ss << test_string.substr(b.first,b.second);
  52.     }
  53.  
  54.     while(it_w != words.rend() || it_s != spaces.end()) {
  55.         if (it_w != words.rend()) {
  56.             b = *it_w++;
  57.             ss << test_string.substr(b.first,b.second);
  58.         }
  59.         if (it_s != spaces.end()) {          
  60.             b = *it_s++;
  61. 		    ss << test_string.substr(b.first,b.second);
  62.         }
  63.     }
  64.  
  65.     string reversed = ss.str();
  66.     cout << "Input: '" << test_string << "'" << endl << "Output: '" << reversed << "'" << endl;
  67. }
Success #stdin #stdout 0.01s 2820KB
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Standard input is empty
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Input: ' This   is my test    string'
Output: ' string   test my is    This'
https://ideone.com/2uw9e
language:
C++ (gcc 8.3)
created:
11 years ago
visibility:
secret

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