foo.cc: In function 'void dfs(int, int)':
foo.cc:17:5: error: 't' was not declared in this scope
  if(t==n)
     ^
foo.cc:23:19: error: 't' was not declared in this scope
    dfs(10*s+i,j+1,t+1);
                   ^

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