Company Queries II

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

const int LOG = 18;          
int up[LOG][200005];         // up[j][x] = ancestor(x, 2^j)
int depth[200005];

int ancestor(int x, int k) {
    for (int j = 0; j < LOG && x; j++)
        if (k >> j & 1) x = up[j][x];
    return x;
}

int lca(int a, int b) {
    if (depth[a] < depth[b]) swap(a, b);
    a = ancestor(a, depth[a] - depth[b]);       
    if (a == b) return a;
    for (int j = LOG - 1; j >= 0; j--)  
        if (up[j][a] != up[j][b]) a = up[j][a], b = up[j][b];
    return up[0][a];
}

int main() {
    int n, q;
    cin >> n >> q;
    for (int i = 2; i <= n; i++) {
        cin >> up[0][i];
        depth[i] = depth[up[0][i]] + 1;
    }
    for (int j = 1; j < LOG; j++)
        for (int x = 1; x <= n; x++)
            up[j][x] = up[j-1][up[j-1][x]];
    while (q--) {
        int a, b;
        cin >> a >> b;
        cout << lca(a, b) << endl;
    }
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED