Company Queries II

#include <iostream>
#include <vector>
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 node, int parent) {
    up[node][0] = parent; 
    for (int i = 1; i < LOG; i++) {
        if (up[node][i-1] != -1) {
            up[node][i] = up[up[node][i-1]][i-1]; 
        } else {
            up[node][i] = -1;
        }
    }
    
    for (int neighbor : adj[node]) {
        if (neighbor != parent) {
            depth[neighbor] = depth[node] + 1;
            dfs(neighbor, node);
        }
    }
}

int lca(int u, int v) {
    if (depth[u] < depth[v])
        swap(u, v);
    
    int diff = depth[u] - depth[v];
    for (int i = 0; i < LOG; i++) {
        if ((diff >> i) & 1) {
            u = up[u][i];
        }
    }

    if (u == v) return u;

    for (int i = LOG - 1; i >= 0; i--) {
        if (up[u][i] != up[v][i]) {
            u = up[u][i];
            v = up[v][i];
        }
    }
    
    return up[u][0];
}

int main() {
    int n, q;
    cin >> n >> q;

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

    for (int i = 1; i <= n; i++) {
        for (int j = 0; j < LOG; j++) {
            up[i][j] = -1;
        }
    }

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

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