Company Queries II

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

const int MAXN = 200005;
const int LOG = 18;

int n, q;
vector<int> adj[MAXN];
int up[MAXN][LOG];
int depth[MAXN];

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

int get_lca(int a, int b) {
    if (depth[a] < depth[b]) swap(a, b);
    for (int i = LOG - 1; i >= 0; i--) {
        if (depth[a] - (1 << i) >= depth[b]) {
            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_base::sync_with_stdio(false);
    cin.tie(NULL);

    if (!(cin >> n >> q)) return 0;

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

    dfs(1, -1, 0);

    while (q--){
        int a, b;
        cin >> a >> b;
        cout << get_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