Company Queries II

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

class CompanyHierarchy {
private:
    const int LOG = 20;  // log2(200000) ~ 17, so 20 is a safe value
    vector<vector<int>> adj;  // adjacency list for the hierarchy
    vector<vector<int>> parent;  // parent table for binary lifting
    vector<int> depth;  // depth of each employee

    // DFS to populate parent and depth arrays
    void dfs(int node, int par) {
        parent[node][0] = par;  // direct parent of node
        for (int i = 1; i < LOG; i++) {
            parent[node][i] = parent[parent[node][i-1]][i-1];
        }
        for (int child : adj[node]) {
            if (child != par) {
                depth[child] = depth[node] + 1;
                dfs(child, node);
            }
        }
    }

    // Binary lifting to find the lowest common ancestor
    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 & (1 << i)) {
                u = parent[u][i];
            }
        }

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

        return parent[u][0]; 
    }

public:
    CompanyHierarchy(int n) {
        adj.resize(n + 1);  // employee numbers from 1 to n
        parent.assign(n + 1, vector<int>(LOG));  // binary lifting table
        depth.resize(n + 1);  // depth array
    }

    // Add an employee and their boss relationship
    void add_employee(int employee, int boss) {
        adj[boss].push_back(employee);  
    }

    // Preprocess the hierarchy starting from the general director (node 1)
    void preprocess() {
        depth[1] = 0;  
        dfs(1, 0);  
    }

    // Answer a query about the lowest common boss
    int query(int a, int b) {
        return lca(a, b);  
    }
};

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

    // Create the company hierarchy object
    CompanyHierarchy company(n);

    // Read the hierarchy
    for (int i = 2; i <= n; i++) {
        int boss;
        cin >> boss;
        company.add_employee(i, boss);
    }

    // Preprocess to prepare for LCA queries
    company.preprocess();

    while (q--) {
        int a, b;
        cin >> a >> b;
        cout << company.query(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