Cod sursa(job #3348874)

Utilizator Dia3141Costea Diana Stefania Dia3141 Data 24 martie 2026 15:24:59
Problema Lowest Common Ancestor Scor 100
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 0.92 kb
#include <fstream>
#include <vector>
#define nmax 100001
using namespace std;
ifstream cin("lca.in");
ofstream cout("lca.out");
int st[nmax],dr[nmax],n,m,rmq[nmax][18],k,x,y;
vector<int>v[nmax];
bool is_dad(int x,int y){
    return st[x]<=st[y]&&dr[y]<=dr[x];
}
void dfs(int nod){
    st[nod]=++k;
    for(auto i:v[nod])
        dfs(i);
    dr[nod]=++k;
}
int lca(int x,int y){
    if(is_dad(x,y))
        return x;
    if(is_dad(y,x))
        return y;
    for(int i=17;i>=0;i--)
        if(rmq[x][i]!=0&&!is_dad(rmq[x][i],y))
            x=rmq[x][i];
    return rmq[x][0];
}
int main()
{
    cin>>n>>m;
    for(int i=2;i<=n;i++){
        cin>>rmq[i][0];
        v[rmq[i][0]].push_back(i);
    }
    dfs(1);
    for(int i=1;i<18;i++)
        for(int j=1;j<=n;j++)
            rmq[j][i]=rmq[rmq[j][i-1]][i-1];
    while(m--){
        cin>>x>>y;
        cout<<lca(x,y)<<'\n';
    }
    return 0;
}