foo.cc: In function 'int find_pre(int)':
foo.cc:8:2: warning: this 'if' clause does not guard... [-Wmisleading-indentation]
  if(pre[x] == x)
  ^~
foo.cc:10:3: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'
   return pre[x] = find_pre(pre[x]);
   ^~~~~~

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