Cod sursa(job #3321994)

Utilizator Lex._.Lex Guiman Lex._. Data 12 noiembrie 2025 08:40:07
Problema Lowest Common Ancestor Scor 100
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 1.43 kb
#include <bits/stdc++.h>
#define NMAX 100001
#define LOG 20
using namespace std;

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

vector<int> fii[NMAX];
int nivel[NMAX];
int stra[LOG][NMAX];

void dfs(int nod)
{
    for(auto& fiu : fii[nod])
    {
        nivel[fiu]=1+nivel[nod];
        dfs(fiu);
    }
}

int up(int nod, int k) ///returneaza al k-lea stramos al lui nod
{
    for(int e=LOG-1; e>=0; e--)
    {
        if((1<<e)<=k)
        {
            nod=stra[e][nod];
            k-=(1<<e);
        }
    }
    return nod;
}

int lca(int nod1, int nod2)
{
    if(nivel[nod1]<nivel[nod2]) swap(nod1, nod2);
    if(nivel[nod1]<nivel[nod2]) swap(nod1, nod2);
    nod1=up(nod1, nivel[nod1]-nivel[nod2]); ///aducem cele doua noduri la acelasi nivel

    if(nod1==nod2) return nod1;

    for(int e=LOG-1; e>=0; e--)
    {
        if(stra[e][nod1]!=stra[e][nod2])
        {
            nod1=stra[e][nod1];
            nod2=stra[e][nod2];
        }
    }
    return stra[0][nod1];
}

int main()
{
    int n, m;
    in >> n >> m;
    for(int i=2; i<=n; i++)
    {
        in >> stra[0][i];
        fii[stra[0][i]].push_back(i);
    }

    for(int e=1; e<LOG; e++)
    {
        for(int i=1; i<=n; i++)
            stra[e][i]=stra[e-1][stra[e-1][i]];
    }
    dfs(1);
    while(m--)
    {
        int u, v;
        in >> u >> v;
        out << lca(u, v) << "\n";
    }

    return 0;
}