foo.cc: In function 'void f(int)':
foo.cc:17:3: warning: 'maxn' may be used uninitialized in this function [-Wmaybe-uninitialized]
   if(a[i]==maxn)cout<<i;}
   ^~

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