foo.cc: In function 'long long int solve(int, int)':
foo.cc:16:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
 for(int i=0;i<v[nw].size();i++){
             ~^~~~~~~~~~~~~
foo.cc:22:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
 for(int i=0;i<v[nw].size();i++){
             ~^~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:37:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf(" %lld",&ar[i]);
         ~~~~~^~~~~~~~~~~~~~~~
foo.cc:41:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf(" %d",&t);
         ~~~~~^~~~~~~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。