//AC
for (int j = lt; j <= rt; j ++) {
   Queries i = f[j];
   if (i.id <= mid and find (i.a) == find (i.b)) f1[++ cnt1] = i;
   else f2[++ cnt2] = i;
}

和

//TLE
for (int j = lt; j <= rt; j ++) {
   Queries i = f[j];
   if (i.id > mid) f2[++ cnt2] = i;
   else {
      int x = find (i.a), y = find (i.b);
      if (x == y) f1[++ cnt1] = i;
      else f2[++ cnt2] = i;
   } 
}

有什么区别，为什么一个AC一个TLE