Cod sursa(job #1520691)

Utilizator cristibogdanPatrascu Cristian cristibogdan Data 9 noiembrie 2015 11:10:53
Problema Lowest Common Ancestor Scor 100
Compilator cpp Status done
Runda Arhiva educationala Marime 0.85 kb
#include <fstream>
#include <vector>
using namespace std;
ifstream f("lca.in");
ofstream g("lca.out");
int rmq[20][200005],nr,i,x,n,m,p[100005],l[200005],d,y,j,q;
vector <int> G[100005];
void dfs(int x)
{
    rmq[0][++nr]=x;
    if(!p[x])
        p[x]=nr;
    for(int i=0;i<G[x].size();i++)
    {
        dfs(G[x][i]);
        rmq[0][++nr]=x;
    }
}
int main()
{
    f>>n>>m;
    for(i=2;i<=n;i++)
    {
        f>>x;
        G[x].push_back(i);
    }
    dfs(1);
    l[1]=0;
    for(i=2;i<=nr;i++)
        l[i]=l[i/2]+1;
    for(i=1;(1<<i)<=nr;i++)
        for(j=1;j<=nr;j++)
             rmq[i][j]=min(rmq[i-1][j],rmq[i-1][j+(1<<(i-1))]);
    for(i=1;i<=m;i++)
    {
        f>>x>>y;
        if(p[x]>p[y])
         swap(x,y);
        d=l[p[y]-p[x]];
        g<<min(rmq[d][p[x]],rmq[d][p[y]-(1<<d)+1])<<'\n';
    }
    return 0;
}