Company Queries II

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

// Maximum number of nodes
const int MAX = 200005;
// Maximum number of levels for Binary Lifting (2^20 > 1e6)
const int LOG = 20;

int n, q;
vector<vector<int>> adj(MAX);
int up[MAX][LOG]; // up[v][k] is the 2^k-th ancestor of v
int depth_node[MAX];

// DFS to compute depth and up tables
void dfs(int v, int parent_v) {
    up[v][0] = parent_v;
    for(int k = 1; k < LOG; k++) {
        if(up[v][k-1] != -1)
            up[v][k] = up[ up[v][k-1] ][k-1];
        else
            up[v][k] = -1;
    }
    for(auto &u : adj[v]) {
        if(u != parent_v) {
            depth_node[u] = depth_node[v] + 1;
            dfs(u, v);
        }
    }
}

// Function to compute LCA of a and b
int lca(int a, int b) {
    if(depth_node[a] < depth_node[b])
        swap(a, b);
    // Bring a to the same depth as b
    int k = LOG - 1;
    for(; k >=0; k--) {
        if(up[a][k] != -1 && depth_node[ up[a][k] ] >= depth_node[b])
            a = up[a][k];
    }
    if(a == b)
        return a;
    // Now lift both a and b together
    for(int k = LOG -1; k >=0; k--) {
        if(up[a][k] != -1 && up[a][k] != up[b][k]) {
            a = up[a][k];
            b = up[b][k];
        }
    }
    return up[a][0];
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(NULL);
    cin >> n >> q;
    // Read e_2 to e_n
    for(int i = 2; i <= n; i++) {
        int boss;
        cin >> boss;
        adj[boss].push_back(i);
        adj[i].push_back(boss);
    }
    // Initialize
    depth_node[1] = 0;
    dfs(1, -1);
    // Process queries
    while(q--){
        int a, b;
        cin >> a >> b;
        cout << lca(a, b) << "\n";
    }
}

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