Compilare: main.cpp: In function 'int main()': main.cpp:62:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if ( ans.size() <= k ) ~~~~~~~~~~~^~~~ main.cpp:65:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for ( i = 0 ; i < ans.size() ; ++ i ) out << ans[ i].first.second << ' ' << ans[i].first.first << ' ' << ans[i].second.second << ' ' << ans[i].second.first << '\n' ; ~~^~~~~~~~~~~~