Company Queries II

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

const int LOG = 18;

void build(int n, vector<vector<int>>& up) {
    for (int k = 1; k < LOG; k++) {
        for (int v = 1; v <= n; v++) {
            up[k][v] = up[k - 1][up[k - 1][v]];
        }
    }
}

int lift(int v, int d, const vector<vector<int>>& up) {
    for (int k = 0; k < LOG; k++) {
        if (d >> k & 1) {
            v = up[k][v];
        }
    }
    return v;
}

int lca(int a, int b, const vector<vector<int>>& up, const vector<int>& depth) {
    if (depth[a] < depth[b]) {
        swap(a, b);
    }

    a = lift(a, depth[a] - depth[b], up);
    if (a == b) {
        return a;
    }

    for (int k = LOG - 1; k >= 0; k--) {
        if (up[k][a] != up[k][b]) {
            a = up[k][a];
            b = up[k][b];
        }
    }
    return up[0][a];
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int n, q;
    cin >> n >> q;

    vector<vector<int>> up(LOG, vector<int>(n + 1));
    vector<int> depth(n + 1, 0);

    up[0][1] = 1;
    for (int i = 2; i <= n; i++) {
        cin >> up[0][i];
        depth[i] = depth[up[0][i]] + 1;
    }

    build(n, up);

    while (q--) {
        int a, b;
        cin >> a >> b;
        cout << lca(a, b, up, depth) << "\n";
    }

    return 0;
}

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