Compilare: main.cpp: In function 'int main()': main.cpp:17:54: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while ( !st.empty() and st.size() + n - i -1 >= k and st.top() < ch ) ~~~~~~~~~~~~~~~~~~~~~^~~~ main.cpp:19:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if( st.size() < k) ~~~~~~~~~~^~~