/in/foo.cc: In function 'void updata()':
/in/foo.cc:68:34: error: reference to 'prev' is ambiguous
  for(int i = t; i != s; i = from[prev[i]])
                                  ^~~~
/in/foo.cc:63:5: note: candidates are: int prev [166]
 int prev[maxn + 1 + 5];
     ^~~~