Compilare: In file included from /usr/include/c++/6/cassert:44:0, from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:33, from main.cpp:1: main.cpp: In function 'int32_t main()': main.cpp:58:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] assert(ans.size() < k); ~~~~~~~~~~~^~~ main.cpp: In function 'void IOfile()': main.cpp:19:34: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("alibaba.in", "r", stdin); ^ main.cpp:20:36: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("alibaba.out", "w", stdout); ^