Cod sursa(job #2286779)

Utilizator RaduXD1Nicolae Radu RaduXD1 Data 20 noiembrie 2018 18:57:09
Problema Lowest Common Ancestor Scor 0
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 0.88 kb
#include <fstream>
#include <cstring>
#include <vector>
using namespace std;
ifstream fin("lca.in");
ofstream fout("lca.out");
int i,n,m,nod,poz,j,t[18][100001],lv[100001],aux,a,b;
vector<int> v[100001];
int lca(int a,int b)
{
    int i;
    if(lv[a]<lv[b])swap(a,b);
    aux=lv[a]-lv[b];
    for(i=0;(1<<i)<=aux;i++)if((aux&(1<<i))==1)a=t[i][a];
    for(i=0;(1<<i)<lv[b];i++);
    if(a==b)return a;
    for(i--;i>=0;i--)
        if(t[i][a]&&t[i][a]!=t[i][b]) a=t[i][a],b=t[i][b];
    return t[0][a];
}
void dfs(int nod, int lvl)
{
    lv[nod]=lvl;
    for(int i=0;i<v[nod].size();i++)
        dfs(v[nod][i],lvl+1);
}
int main(){
    fin>>n>>m;
    for(i=2;i<=n;i++){fin>>t[0][i];v[t[0][i]].push_back(i);}
    for(i=1,aux=2;aux<=n;i++,aux<<=1)for(j=1;j<=n;j++)t[i][j]=t[i-1][t[i-1][j]];
    dfs(1,1);
    for(i=1;i<=m;i++){fin>>a>>b;fout<<lca(a,b)<<"\n";}
    return 0;
}