Cod sursa(job #3226555)

Utilizator AndreiBOTOBotocan Andrei AndreiBOTO Data 21 aprilie 2024 21:52:38
Problema Lowest Common Ancestor Scor 100
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 1.41 kb
#include <bits/stdc++.h>

#pragma optimize GCC ("Ofast")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")

///#include <tryhardmode>
///#include <GODMODE::ON>

using namespace std;

#define cin fin
#define cout fout

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

const int NMAX=1e5+5;

vector<int>v[NMAX];

int lvl[NMAX];
int asc[25][NMAX];

void dfs(int p,int tata)
{
    int e;
    lvl[p]=lvl[tata]+1;
    for(e=1;e<=20;e++)
        asc[e][p]=asc[e-1][asc[e-1][p]];
    for(auto i:v[p])
    {
        if(i!=tata)
        {
            asc[0][i]=p;
            dfs(i,p);
        }
    }
}

int lca(int x,int y)
{
    int level,e;
    if(lvl[x]<lvl[y])
        swap(x,y);
    level=lvl[x]-lvl[y];
    for(e=20;e>=0;e--)
        if(level & (1<<e))
            x=asc[e][x];
    if(x==y)
        return x;
    for(e=20;e>=0;e--)
    {
        if(asc[e][x]!=asc[e][y])
        {
            x=asc[e][x];
            y=asc[e][y];
        }
    }
    return asc[0][x];
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);

    int n,q,i,j;
    cin>>n>>q;
    for(i=2;i<=n;i++)
    {
        int x;
        cin>>x;
        v[i].push_back(x);
        v[x].push_back(i);
    }
    dfs(1,0);
    while(q--)
    {
        int x,y;
        cin>>x>>y;
        cout<<lca(x,y)<<"\n";
    }
    return 0;
}