Compilare: main.cpp: In function 'int main()': main.cpp:15:55: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 15 | while (!ans.empty() && s[i] > ans.back() && k <= n - ans.size()) { | ~~^~~~~~~~~~~~~~~~~ main.cpp:18:24: warning: comparison of integer expressions of different signedness: 'std::vector<char>::size_type' {aka 'long unsigned int'} and 'int' [-Wsign-compare] 18 | if (ans.size() != k) { | ~~~~~~~~~~~^~~~