Company Queries II

// ~/.vim/cpp_template.cpp
#include <bits/stdc++.h>
#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <limits>

#define REP(i,a,b) for (int i = a; i < b; i++)

// Type Aliases for 1D and 2D vectors with initialization
#define vi(n, val) vector<int>(n, val) // 1D vector of ints with size n, initialized to val
#define vll(n, val) vector<long long>(n, val) // 1D vector of long longs with size n, initialized to val
#define ll long long
#define vvi(n, m, val) vector<vector<int>>(n, vector<int>(m, val)) // 2D vector of ints (n x m), initialized to val
#define vvll(n, m, val) vector<vector<long long>>(n, vector<long long>(m, val)) // 2D vector of long longs (n x m), initialized to val

#define LL_INF std::numeric_limits<long long int>::max()
#define INF std::numeric_limits<int>::max()


using namespace std;


template <typename T>
void pV(const std::vector<T>& vec, const std::string& label = "Vector") {
    std::cout << label << ": [ ";
    for (const auto& elem : vec) {
        std::cout << elem << " ";
    }
    std::cout << "]" << std::endl;
}


void dfs(int s, vector<bool> *visited, vector<int> (*adj)[]) {
    if ((*visited)[s]) return;
    (*visited)[s] = true;
    // process node s


    for (auto u: (*adj)[s]) {
        dfs(u, visited, adj);
    }
}
/*
// DEPTH-FRIRST-SEARCH
vector<int> adj[N];                                                          
vector<bool> visited(N, false);
int u, v;
for(int i = 0; i < M;i++){
    cin >> u >> v;
    u--;
    v--;
    adj[u].push_back(v);
    adj[v].push_back(u);
}
*/

vector<long long> dijkstra(int N, int x, vector<vector<pair<int,int>>> *adj){
    vector<bool> processed(N, false);
    vector<long long> distance(N, LL_INF);
    priority_queue<pair<long long,int>> q;
    //for (int i = 1; i <= n; i++) distance[i] = INF;
    distance[x] = 0;
    q.push({0,x});
    while (!q.empty()) {
        int a = q.top().second; q.pop();
        if (processed[a]) continue;
        processed[a] = true;
        for (auto u : (*adj)[a]) {
            int b = u.first, w = u.second;
            if (distance[a]+w < distance[b]) {
                distance[b] = distance[a]+w;
                q.push({-distance[b],b});
            }
        }
    }
    return distance;


}


/*
DIJKSTRA
//vector<vector<pair<int,int>>> adj(N, vector<pair<int, int>>(N));
*/


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 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::sync_with_stdio(0);
    cin.tie(0);
    // Your code starts here
    int n, q;
    cin >> n >> q;
    
    for (int i = 2; i <= n; i++) {
        int b;
        cin >> b;
        adj[b].push_back(i);
        adj[i].push_back(b);
    }

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

    //queries
    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