foo.cc: In function 'int main()':
foo.cc:33:2: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
  for (int i = 1; i <= len1; i++)
  ^~~
foo.cc:36:3: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'for'
   printf("%d\n", f[len1][len2]);
   ^~~~~~

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