Shared code

#include <iostream>
#include <vector>
 
using ll = long long;
 
int const nmax = 200000;
int parent[1 + nmax];
int far[1 + nmax];
int level[1 + nmax];

int getLca(int x, int y) {
  if(level[x] < level[y])
    std::swap(x, y);
  while(level[y] < level[x]) {
    if(level[y] <= level[far[x]])
      x = far[x];
    else
      x = parent[x];
  }

  if(x == y)
    return x;
  while(parent[x] != parent[y]) {
    if(far[x] != far[y]) {
      x = far[x];
      y = far[y];
    } else {
      x = parent[x];
      y = parent[y];
    }
  }
  return parent[x];
}
  
int main() {
  int n, q;
  std::cin >> n >> q;
  for(int i = 2; i <= n; i++)
    std::cin >> parent[i];
  level[1] = 1;
  for(int i = 2; i <= n; i++) {
    level[i] = level[parent[i]] + 1;
    int father = parent[i];
    int father2 = far[father];
    if(far[father2] != 0 && level[father] - level[father2] == level[father2] - level[far[father2]]) {
      far[i] = far[father2];
    } else
      far[i] = father;
  }

  for(int i = 1;i <= q; i++) {
    int x, y;
    std::cin >> x >> y;
    std::cout << getLca(x, y) << '\n';
  }
  return 0;
}