foo.cc: In function 'void dfs(int)':
foo.cc:30:37: warning: this 'else' clause does not guard... [-Wmisleading-indentation]
     if(k==n-1)if(check())out();else;else;
                                     ^~~~
foo.cc:31:9: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'else'
         for(int i=1;i<n;i++)if(v[i]==-1)v[i]=k,dfs(k+1),v[i]=-1;
         ^~~
foo.cc: In function 'int main()':
foo.cc:35:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d",&n);
     ~~~~~^~~~~~~~~
foo.cc:44:18: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
             scanf("%s",s+1);
             ~~~~~^~~~~~~~~~

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

{"receive":"2020-07-03T15:29:33.166Z","handle":"2020-07-03T15:29:33.166Z","cache_start":"2020-07-03T15:29:33.176Z","read_cases":"2020-07-03T15:29:33.296Z","judge":"2020-07-03T15:29:33.296Z","done":"2020-07-03T15:29:35.252Z"}