Compilare: main.cpp: In function 'bool is_valid(int, int, std::vector<int>&)': main.cpp:8:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=1; i<ys.size(); ++i) { ~^~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:48:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=1; i<solutions.size(); ++i) { ~^~~~~~~~~~~~~~~~~ main.cpp:36:35: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("damesah.in", "r", stdin); ^ main.cpp:37:37: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("damesah.out", "w", stdout); ^ main.cpp:40:17: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &n); ^