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#include <iostream>
#include <vector>
 
// Write a program that outputs all possibilities to put + or - or nothing 
// between the numbers 1, 2, ..., 9 (in this order) such that the result is 
// always 100. For example: 1 + 2 + 34 – 5 + 67 – 8 + 9 = 100.
 
enum class Operation {
	Nothing,
	Add,
	Substract
};
 
// Produce the next vector of Operations
// \returns "true" if a vector was produced, "false" otherwise
bool next(std::vector<Operation>& operations) {
	for (Operation& o: operations) {
		switch (o) {
		case Operation::Nothing:
			o = Operation::Add;
			return true;
		case Operation::Add:
			o = Operation::Substract;
			return true;
		case Operation::Substract:
			o = Operation::Nothing;
			break; // loop to increment next
		}
	}
	return false; // if we reach here, the vector is not long enough
} // next
 
// Given a list of integers and operations, return the total
int compute(std::vector<int> const& suite,
		    std::vector<Operations> const& operations)
{
	// 1. First pass, group by nothing
	std::vector<int> catenated{1, suite[0]};
 
	for (size_t i = 0, max = operations.size(); i < max; ++i) {
		if (operations[i] != Operation::Nothing) {
			catenated.push_back(suite[i+1]);
			continue;
		}
 
		int& last = catenated.back();
		last *= 10;
		last += suite[i+1];
	}
 
	// 2. Second pass, evaluate
	int total = catenated[0]; catenated.pop();
 
	for (Operation const& o: operations) {
		switch (o) {
		case Operation::Nothing: break;
 
		case Operation::Add:
			total += catenated[0]; catenated.pop();
			break;
 
		case Operation::Substract:
			total -= catenated[0]; catenated.pop();
			break;
		}
	}
 
	return total;
} // compute
 
// Display the list of "+- " and its result
void display(std::vector<int> const& suite,
		     std::vector<Operations> const& operations,
		     int const target)
{
	std::cout << suite[0];
	for (size_t i = 0, max = operations.size(); i < max; ++i) {
		switch (operations[i]) {
		case Operation::Nothing: break;
 
		case Operation::Add: std::cout << " + "; break;
 
		case Operation::Substract: std::cout << " - "; break;
		}
 
		std::cout << suite[i + 1];
	}
 
	std::cout << " = " << target << "\n";
} // display
 
// Output the lists of "+- " which achieve the goal for the given vector and the
// given target number.
void compute(std::vector<int> const& suite, int const target) {
	if (suite.empty()) { return; }
 
	Operation const N = Operation::Nothing;
	std::vector<Operation> operations{suite.size() - 1, N};
 
	do {
		if (compute(suite, operations) == target) {
			display(suite, operations, target);
		}
	} while (next(operations));
}
 
int main() {
	std::vector<int> vec{1, 2, 3, 4, 5, 6, 7, 8, 9};
	compute(vec, 100);
	return 0;
}

Main.java:1: error: illegal character: '#'
#include <iostream>
^
Main.java:1: error: class, interface, or enum expected
#include <iostream>
         ^
Main.java:2: error: illegal character: '#'
#include <vector>
^
Main.java:8: error: <identifier> expected
enum class Operation {
    ^
Main.java:9: error: <identifier> expected
	Nothing,
	       ^
Main.java:11: error: ';' expected
	Substract
	         ^
Main.java:16: error: <identifier> expected
bool next(std::vector<Operation>& operations) {
             ^
Main.java:16: error: ';' expected
bool next(std::vector<Operation>& operations) {
               ^
Main.java:16: error: illegal start of type
bool next(std::vector<Operation>& operations) {
                                ^
Main.java:16: error: '(' expected
bool next(std::vector<Operation>& operations) {
                                  ^
Main.java:16: error: illegal start of type
bool next(std::vector<Operation>& operations) {
                                            ^
Main.java:16: error: <identifier> expected
bool next(std::vector<Operation>& operations) {
                                             ^
Main.java:16: error: ';' expected
bool next(std::vector<Operation>& operations) {
                                               ^
Main.java:17: error: illegal start of type
	for (Operation& o: operations) {
	    ^
Main.java:17: error: ';' expected
	for (Operation& o: operations) {
	              ^
Main.java:17: error: <identifier> expected
	for (Operation& o: operations) {
	                 ^
Main.java:17: error: <identifier> expected
	for (Operation& o: operations) {
	                             ^
Main.java:30: error: illegal start of type
	return false; // if we reach here, the vector is not long enough
	^
Main.java:30: error: ';' expected
	return false; // if we reach here, the vector is not long enough
	      ^
Main.java:34: error: class, interface, or enum expected
int compute(std::vector<int> const& suite,
^
Main.java:40: error: class, interface, or enum expected
	for (size_t i = 0, max = operations.size(); i < max; ++i) {
	^
Main.java:40: error: class, interface, or enum expected
	for (size_t i = 0, max = operations.size(); i < max; ++i) {
	                                            ^
Main.java:40: error: class, interface, or enum expected
	for (size_t i = 0, max = operations.size(); i < max; ++i) {
	                                                     ^
Main.java:43: error: class, interface, or enum expected
			continue;
			^
Main.java:44: error: class, interface, or enum expected
		}
		^
Main.java:47: error: class, interface, or enum expected
		last *= 10;
		^
Main.java:48: error: class, interface, or enum expected
		last += suite[i+1];
		^
Main.java:49: error: class, interface, or enum expected
	}
	^
Main.java:52: error: class, interface, or enum expected
	int total = catenated[0]; catenated.pop();
	                          ^
Main.java:54: error: class, interface, or enum expected
	for (Operation const& o: operations) {
	^
Main.java:58: error: class, interface, or enum expected
		case Operation::Add:
		^
Main.java:59: error: class, interface, or enum expected
			total += catenated[0]; catenated.pop();
			                       ^
Main.java:60: error: class, interface, or enum expected
			break;
			^
Main.java:62: error: class, interface, or enum expected
		case Operation::Substract:
		^
Main.java:63: error: class, interface, or enum expected
			total -= catenated[0]; catenated.pop();
			                       ^
Main.java:64: error: class, interface, or enum expected
			break;
			^
Main.java:65: error: class, interface, or enum expected
		}
		^
Main.java:69: error: class, interface, or enum expected
} // compute
^
Main.java:77: error: class, interface, or enum expected
	for (size_t i = 0, max = operations.size(); i < max; ++i) {
	^
Main.java:77: error: class, interface, or enum expected
	for (size_t i = 0, max = operations.size(); i < max; ++i) {
	                                            ^
Main.java:77: error: class, interface, or enum expected
	for (size_t i = 0, max = operations.size(); i < max; ++i) {
	                                                     ^
Main.java:81: error: class, interface, or enum expected
		case Operation::Add: std::cout << " + "; break;
		^
Main.java:81: error: class, interface, or enum expected
		case Operation::Add: std::cout << " + "; break;
		                                         ^
Main.java:83: error: class, interface, or enum expected
		case Operation::Substract: std::cout << " - "; break;
		^
Main.java:83: error: class, interface, or enum expected
		case Operation::Substract: std::cout << " - "; break;
		                                               ^
Main.java:84: error: class, interface, or enum expected
		}
		^
Main.java:87: error: class, interface, or enum expected
	}
	^
Main.java:90: error: class, interface, or enum expected
} // display
^
Main.java:95: error: class, interface, or enum expected
	if (suite.empty()) { return; }
	                             ^
Main.java:98: error: class, interface, or enum expected
	std::vector<Operation> operations{suite.size() - 1, N};
	^
Main.java:100: error: class, interface, or enum expected
	do {
	^
Main.java:103: error: class, interface, or enum expected
		}
		^
Main.java:105: error: class, interface, or enum expected
}
^
Main.java:109: error: class, interface, or enum expected
	compute(vec, 100);
	^
Main.java:110: error: class, interface, or enum expected
	return 0;
	^
Main.java:111: error: class, interface, or enum expected
}
^
56 errors

Standard output is empty