Company Queries II

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

const int MAXN = 200005;
const int LOG = 20;
vector<int> adj[MAXN];
int up[MAXN][LOG];
int depth[MAXN];

void dfs(int v, int parent) {
    up[v][0] = parent;
    for (int i = 1; i < LOG; i++) {
        up[v][i] = up[up[v][i-1]][i-1];
    }
    for (int u : adj[v]) {
        if (u != parent) {
            depth[u] = depth[v] + 1;
            dfs(u, v);
        }
    }
}

int lca(int a, int b) {
    if (depth[a] < depth[b]) swap(a, b);

    int diff = depth[a] - depth[b];
    for (int i = 0; i < LOG; i++) {
        if ((diff >> i) & 1) {
            a = up[a][i];
        }
    }

    if (a == b) return a;

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

    return up[a][0];
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);

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

    for (int i = 2; i <= n; i++) {
        int boss;
        cin >> boss;
        adj[boss].push_back(i);
        adj[i].push_back(boss);
    }

    depth[1] = 0;
    dfs(1, 1);

    while (q--) {
        int a, b;
        cin >> a >> b;
        cout << lca(a, b) << '\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