Cod sursa(job #1646885)

Utilizator george_stelianChichirim George george_stelian Data 10 martie 2016 18:06:10
Problema Lowest Common Ancestor Scor 70
Compilator cpp Status done
Runda Arhiva educationala Marime 1.06 kb
#include <cstdio>
#include <vector>

using namespace std;

vector<int> v[100010];
int niv[100010],tata[20][100010],logn;

void dfs(int nod,int dad,int lev)
{
    tata[0][nod]=dad;
    niv[nod]=lev;
    for(int i=1;i<=logn;i++) tata[i][nod]=tata[i-1][tata[i-1][nod]];
    for(vector<int>::iterator it=v[nod].begin();it!=v[nod].end();it++)
        dfs(*it,nod,lev+1);
}

int lca(int x,int y)
{
    if(niv[x]<niv[y]) swap(x,y);
    for(int i=logn;i>=0;i--)
        if(niv[tata[i][x]]>=niv[y]) x=tata[i][x];
    for(int i=logn;i>=0;i--)
        if(tata[i][x]!=tata[i][y]) {x=tata[i][x];y=tata[i][y];}
    if(x==y) return x;
    else return tata[0][x];
}

int main()
{
    freopen("lca.in", "r", stdin);
    freopen("lca.out", "w", stdout);
    int n,m,x,y;
    scanf("%d%d",&n,&m);
    for(int i=2;i<=n;i++)
    {
        scanf("%d",&x);
        v[x].push_back(i);
    }
    for(logn=1;1<<logn<=n;logn++);logn--;
    dfs(1,0,1);
    for(int i=1;i<=m;i++)
    {
        scanf("%d%d",&x,&y);
        printf("%d\n",lca(x,y));
    }
    return 0;
}