Compilare: main.cpp: In function 'void mergeTreaps(int, int, std::vector<int>&)': main.cpp:139:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i<arr.size(); i++) { ~^~~~~~~~~~~ main.cpp: In function 'void dfs(int, int)': main.cpp:157:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i<to_erase.size(); i++) { ~^~~~~~~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:165:33: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("metro.in","r", stdin); ^ main.cpp:166:35: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("metro.out","w", stdout); ^