Cod sursa(job #3148077)

Utilizator TeodoraMaria123Serban Teodora Maria TeodoraMaria123 Data 29 august 2023 12:04:31
Problema Stramosi Scor 100
Compilator cpp-64 Status done
Runda Arhiva de probleme Marime 1.58 kb
#include <bits/stdc++.h>

using namespace std;

#define MAX_N 250000
#define pb push_back

int n, m, L;
bitset <MAX_N + 1> viz;
vector <vector <int> > up, graph;

void dfs(int node, int parent)
{
//    cout << node << " ";
    viz[node] = 1;
    up[0][node] = parent;
    for(int i = 1; i <= L; i ++)
        up[i][node] = up[i - 1][up[i - 1][node]];

    for(auto x : graph[node])
    {
        if(!viz[x])
            dfs(x, node);
    }
}

int ancestor(int a, int b)
{
    for(int i = L; i >= 0; i --)
    {
        if(b >= (1 << i))
        {
            a = up[i][a];
            b -= (1 << i);
        }
    }
    return a;
}

int main()
{
    ios_base :: sync_with_stdio(0);
    cin.tie(0);

    freopen("stramosi.in", "r", stdin);
    freopen("stramosi.out", "w", stdout);

    cin >> n >> m;
    graph.resize(n + 1);
    L = log2(n);
    up.assign(L + 1, vector <int> (n + 1));

    for(int i = 1; i <= n; i ++)
    {
        int x;
        cin >> x;
        graph[x].pb(i);
    }

    dfs(0, 0);
//    cout << "\n";
//
//    for(int node = 1; node <= n; node ++)
//    {
//        cout << node << "\n";
//        for(int i = 0; i <= L; i ++)
//            cout << i << " " << up[node][i] << "\n";
//        cout << "\n";
//    }

//    for(int node = 1; node <= n; node ++)
//    {
//        for(int i = 1; i <= L; i ++)
//            up[node][i] = up[up[node][i - 1]][i - 1];
//    }

    for(int i = 1; i <= m; i ++)
    {
        int a, b;
        cin >> a >> b;
        cout << ancestor(a, b) << "\n";
    }
    return 0;
}