Shared code

#include<bits/stdc++.h>
using namespace std;
 
typedef long long int ll;
#define IOS ios_base::sync_with_stdio(0);  cin.tie(0); cout.tie(0);
 
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
 
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>order_set;
typedef pair<int, int>pr;
#define all(i)     i.begin() , i.end()
#define ft     first
#define sn     second
#define pb push_back
 
#define totalone(mask) __builtin_popcount(mask)
#define chkbit(mask,bit) (mask&(1LL << bit))
#define setbit(mask,bit) (mask|(1LL << bit))
#define cngbit(mask,bit) (mask^(1LL << bit))
 
#define en "\n"
#define dbg(x) cerr<<#x<<" is : "<<x<<en;
#define yes cout<<"YES\n"
#define no cout<<"NO\n"
#define report cout<<-1<<en
#define sum(n) ((1LL*(n)*(n+1))/ 2LL)
#define sqr(n) (1LL*(n)*(n))
#define vag(a,b) ((a + b - 1)/b)
#define coutv(v) for(auto i: v) cout<<i<<" ";cout<<en;
#define cinv(v) for(auto &i: v) cin >> i;
 
const int MAXN = 200005;
#define inf 1e15
const int mod = 1e9 + 7;
 
int n, q;
int up[MAXN][20];
int dis[MAXN];
int vis[MAXN];
vector<int>g[MAXN];
 
void dfs(int nd)
{
    vis[nd] = 1;
    for (auto i : g[nd])
    {
        if (vis[i]) continue;
        dis[i] = 1 + dis[nd];
        for (int log = 1; log < 20; log++)
        {
            int ancestor = up[i][log - 1];
            up[i][log] = up[ancestor][log - 1];
        }
        dfs(i);
    }
}
 
int get_lca(int x, int y)
{
    if (dis[x] < dis[y]) swap(x, y); //let, x is max always
    int k = dis[x] - dis[y];
    for (int log = 19; log >= 0; log--)
    {
        if (chkbit(k, log)) {
            x = up[x][log];
        }
    }
    if (x == y) return x;
 
    for (int log = 19; log >= 0; log--)
    {
        if (up[x][log] != up[y][log]) {
            x = up[x][log];
            y = up[y][log];
        }
    }
 
    return up[x][0];
}
void solve()
{
    cin >> n >> q;
    for (int i = 2; i <= n; i++)
    {
        cin >> up[i][0];
        int x = up[i][0];
        g[x].pb(i);
        g[i].pb(x);
    }
 
    dfs(1);
 
    // for (int i = 1; i <= n; i++) {
    //     for (int j = 0; j < 3; j++) cout << up[i][j] << " "; cout << en;
    // }
 
    while (q--)
    {
        int x, y;
        cin >>  x >> y;
        cout << get_lca(x, y) << en;
    }
 
}
int main()
{
    IOS;
    ll t;
    t = 1;
    // cin >> t;
 
    int c = 0;
    while ( t-- )
    {
        // cout<<"Case "<<++c<<": ";
        solve();
    }
    return 0;
}