Compilare: user.cpp: In function ‘void dfs(int, int)’: user.cpp:25:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<a[x].size();i++)if(a[x][i]!=p)dfs(a[x][i],x); ~^~~~~~~~~~~~ user.cpp: In function ‘int main()’: user.cpp:41:32: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("lca.in","r",stdin); ^ user.cpp:42:31: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("lca.out","w",stdout); ^