Compilare: user.cpp: In function ‘void backtr(int, int)’: user.cpp:29:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (cnt == sol.size() - 1) ^ user.cpp: In function ‘int main()’: user.cpp:65:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < sol.size(); ++ i) ^ user.cpp:66:51: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] cout << sol[i] << " \n"[i + 1 == sol.size()]; ^