Company Queries II

#include <iostream>
#include <vector>
#include <cmath>

using namespace std;

void dfs(int node, int parent, const vector<vector<int>>& tree, vector<int>& depth, vector<vector<int>>& up, int LOG) {
    up[node][0] = parent;
    for (int i = 1; i <= LOG; ++i) {
        up[node][i] = up[up[node][i - 1]][i - 1];
    }
    for (int child : tree[node]) {
        if (child != parent) {
            depth[child] = depth[node] + 1;
            dfs(child, node, tree, depth, up, LOG);
        }
    }
}

int lca(int a, int b, const vector<int>& depth, const vector<vector<int>>& up, int LOG) {
    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; i >= 0; --i) {
        if (up[a][i] != up[b][i]) {
            a = up[a][i];
            b = up[b][i];
        }
    }
    return up[a][0];
}

int main() {
    int n, q;
    cin >> n >> q;
    
    int LOG = log2(n) + 1;
    vector<vector<int>> tree(n + 1);
    vector<int> depth(n + 1);
    vector<vector<int>> up(n + 1, vector<int>(LOG + 1));
    
    for (int i = 2; i <= n; ++i) {
        int boss;
        cin >> boss;
        tree[boss].push_back(i);
        tree[i].push_back(boss);
    }
    
    depth[1] = 0;
    dfs(1, 1, tree, depth, up, LOG);
    
    while (q--) {
        int a, b;
        cin >> a >> b;
        cout << lca(a, b, depth, up, LOG) << endl;
    }
    
    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