Compilare: main.cpp: In function 'void solve_and_write()': main.cpp:19:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(k = 0; k < G[j].size(); k++) ~~^~~~~~~~~~~~~ main.cpp: In function 'void read_data()': main.cpp:33:29: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d\n", &N, &M); ^ main.cpp:36:31: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d", &a, &b); ^ main.cpp: In function 'int main()': main.cpp:43:40: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("sortaret.in", "rt", stdin); ^ main.cpp:44:42: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("sortaret.out", "wt", stdout); ^