HCM Financial Center

#include<bits/stdc++.h>
using namespace std;

const int N = 1e5 + 5;
int n, q;
vector<int>g[N];
int dep[N];
int parent[N][20];

void dfs(int u, int p){
  parent[u][0] = p;
  for (int v : g[u]){
    if (v == p) continue;
    dep[v] = dep[u] + 1;
    dfs(v, u);
  }
}

int lca(int u, int v){
  if (dep[u] > dep[v]) swap(u, v);
  for (int k = 18; k >= 0; k--) {

    if (dep[parent[v][k]] >= dep[u]) {
      v = parent[v][k];
    }
  }
  for (int k = 18; k >= 0; k--){
    if (parent[u][k] != parent[v][k]){
      u = parent[u][k];
      v = parent[v][k];
    }
  }
  while (u != v) {
    u = parent[u][0];
    v = parent[v][0];
  }
  return u;
}

void preprocess(){
  dep[0] = 0;
  dfs(0, 0);
  for (int k = 1; k <= 18; k++){
    for (int i = 0; i < n; i++){
      parent[i][k] = parent[parent[i][k-1]][k-1];
    }
  }
}

int ans;
void process(int a, int b, int c){
  int ac = lca(a, c);
    int ab = lca(a, b);
    int bc = lca(b, c);
    if (ab == bc){
      if (ac == b){
        ans = max(ans, 1);
      }
      else {
        if (ac != ab){
          int tmp = abs(dep[ab] - dep[b]) + abs(dep[ab] - dep[ac]) + 1;
          ans = max(ans, tmp);
        }
        else {
          ans = max(ans, abs(dep[ac] - dep[b]) + 1);
        }
      }
    }
    else {
      ans = max(ans, 1 + abs(dep[b] - max(dep[ab], dep[bc])));
    }
}

int main(){
  cin >> n >> q;
  for (int i = 1; i < n; i++){
    int x;
    cin >> x;
    x--;
    g[i].push_back(x);
    g[x].push_back(i);
  }
  preprocess();
  while(q--){
    int a, b, c;
    cin >> a >> b >> c;
    a--, b--, c--;

    ans = 0;
    process(a, b, c);
    process(b, a, c);
    process(a, c, b);
    cout << ans << endl;
  }
}