Cod sursa(job #2843120)

Utilizator cezar.balutaCezar Baluta cezar.baluta Data 2 februarie 2022 00:40:37
Problema Lowest Common Ancestor Scor 90
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 1.78 kb
/*
                         __
                   _.--""  |
    .----.     _.-'   |/\| |.--.
    |    |__.-'   _________|  |_)  _______________
    |  .-""-.""""" ___,    `----'"))   __   .-""-.""""--._
    '-' ,--. `    |Cezar| .---.       |:.| ' ,--. `      _`.
     ( (    ) ) __|  7  |__\\|// _..-- \/ ( (    ) )--._".-.
      . `--' ;\__________________..--------. `--' ;--------'
       `-..-'                               `-..-'
 */
#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

const int N = 1e5 + 5;
int stramosi[18][N];
vector<int>a[N];
int nivel[N];
int tata[N];

void nivell(int x, int niv){
    nivel[x] = niv;
    for(auto y:a[x]){
        nivell(y,niv+1);
    }
}

int lca(int x, int y){
    int niv1 = nivel[x];
    int niv2 = nivel[y];
    int p1 = x;
    int p2 = y;
    if(niv1<niv2){
        swap(niv1,niv2);
        swap(p1,p2);
    }
    while(niv1 != niv2){
        p1 = tata[p1];
        niv1 = nivel[p1];
    }
    for(int i = 17;i>=0;i--){
        if(niv1 - (1<<i)>=1 && stramosi[i][p1]!=stramosi[i][p2]){
            p1 = stramosi[i][p1];
            p2 = stramosi[i][p2];
            niv1 = nivel[x];
        }
    }
    if(p1==p2)
        return p1;

    p1 = stramosi[0][p1];
    return p1;

}

int main() {
    ifstream in("lca.in");
    ofstream out("lca.out");
    ios_base::sync_with_stdio(false);
    int n,m;
    in>>n>>m;
    stramosi[0][1] = 1;
    tata[1] = 1;
    for(int i=2;i<=n;i++){
        in>>stramosi[0][i];
        tata[i] = stramosi[0][i];
        a[stramosi[0][i]].push_back(i);
    }
    for(int i=1;i<18;i++){
        for(int j=1;j<=n;j++) {
            stramosi[i][j] = stramosi[i-1][stramosi[i-1][j]];
        }
    }
    nivell(1,1);
    int x,y;
    while(m--){
        in>>x>>y;
        out<<lca(x,y)<<'\n';
    }
    return 0;
}