Cod sursa(job #3041463)

Utilizator PHOSSESSEDProsie Radu-Teodor PHOSSESSED Data 31 martie 2023 15:35:54
Problema Lowest Common Ancestor Scor 100
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 1.14 kb
#include<fstream>
#include<vector>
using namespace std;

ifstream cin("lca.in");
ofstream cout("lca.out");

const int NMAX = 1e5 + 1;
const int logmax = 17;

int lift[logmax + 1][NMAX],level[NMAX];

void go(int i)
{
    if(level[i] || i == 1) return;
    go(lift[0][i]); level[i] = level[lift[0][i]] + 1;
}


int lca(int a,int b)
{
    if(level[a] < level[b]) swap(a,b);
    int diff = level[a] - level[b];
    for(int i = logmax ; i >= 0 ; i--) if(diff & (1 << i)) a = lift[i][a];
    if(a == b) return a;
    for(int h = logmax ; h >= 0 ; h--)
        {
            if(lift[h][a] != lift[h][b])
                {
                    a = lift[h][a];
                    b = lift[h][b];
                }
        }

    return lift[0][a];
}

int main()
{
    int n,q,a,b; cin >> n >> q;
    for(int i = 2; i <= n ; i++) cin >> lift[0][i];
    for(int i = 1; i <= logmax ; i++)
        for(int j = 2; j <= n ; j++)
            lift[i][j] = lift[i - 1][lift[i - 1][j]];

    for(int i = 2; i <= n ; i++) go(i);
    while(q--)
        {
            cin >> a >> b;
            cout << lca(a,b) << '\n';
        }
}