Compilare: user.cpp: In function ‘bool isValid(std::vector<int>&, unsigned int)’: user.cpp:26:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (stack[stack.size() - 1] >= size) return false; user.cpp: In function ‘int main()’: user.cpp:68:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < flippedCols.size(); i++) { ~~^~~~~~~~~~~~~~~~~~~~ user.cpp:104:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < flippedCols.size(); i++) { ~~^~~~~~~~~~~~~~~~~~~~