Cod sursa(job #2240782)

Utilizator AvramDanielAvram Daniel AvramDaniel Data 14 septembrie 2018 00:27:43
Problema Lowest Common Ancestor Scor 0
Compilator cpp Status done
Runda Arhiva educationala Marime 1.49 kb
#include <bits/stdc++.h>
using namespace std;

int n,m,a,poz[1000],x,y,l,k,pozy,pozx,lg[1000],rmq[1000][17];
bool viz[1000];
vector<int>v[1000],eu;

void euler(int x)
{
    if(!viz[x])
    {
        viz[x]=1;
        poz[x]=eu.size()+1;
    }
    eu.push_back(x);
    for(int i=0;i<v[x].size();i++)
    {
        euler(v[x][i]);
        eu.push_back(x);
    }
    return;
}

int main()
{
    ifstream cin("lca.in");
    ofstream cout("lca.out");
    cin>>n>>m;
    lg[1]=0;
    for(int i=2;i<=n;i++)
    {
        cin>>a;
        v[a].push_back(i);
        lg[i]=lg[i/2]+1;
    }
    euler(1);

    for(int i=0;i<eu.size();i++)
    {
        //cout<<eu[i]<<' ';
        rmq[0][i+1]=eu[i];
    }
    //cout<<'\n';
    n=eu.size();
    for(int i=1;(1<<i)<=n;i++)
    {
        for(int j=1;j<=n-(1<<i)+1;j++)
        {
            rmq[i][j]=min(rmq[i-1][j],rmq[i-1][j+(1<<(i-1))]);
            //cout<<rmq[i][j]<<' ';
        }
        //cout<<'\n';
    }
   /* for(int i=0;(1<<i)<=n;i++)
    {
        cout<<'\n';
        for(int j=1;j<=n;j++)
            cout<<rmq[i][j]<<' ';
    }

        cout<<'\n';*/
       // for(int i=1;i<=n;i++)
        //lg[i]=lg[i/2]+1;

    for(;m;m--)
    {
        cin>>x>>y;
        pozx=min(poz[x],poz[y]);
        pozy=max(poz[x],poz[y]);
        l=pozy-pozx+1;
        k=lg[l];
        //cout<<k<<' '<<pozx<<' '<<pozy<<'\n';
        cout<<min(rmq[k][pozx],rmq[k][pozy-(1<<(k))+1])<<'\n';

    }

    return 0;
}