Cod sursa(job #2643515)

Utilizator evelina.nitoiuNitoiu Evelina evelina.nitoiu Data 20 august 2020 09:30:24
Problema Lowest Common Ancestor Scor 100
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 1.09 kb
#include <fstream>
#include <vector>

using namespace std;

ifstream cin("lca.in");
ofstream cout("lca.out");
vector <int> L[100001];
int log;
int n,a,q,viz[100001],v[100001][20],nivel[100001];

void dfs(int x)
{
    a++;
    nivel[x]=a;
    viz[x]=1;
    for(int i=1;i<=log;i++)
        v[x][i]=v[v[x][i-1]][i-1];
    for(int i:L[x])
        if(!viz[i])
            dfs(i);
    a--;
}
int LCA(int x,int y)
{
    int p=log;
    if(nivel[x]>nivel[y])
        swap(x,y);
    while(nivel[y]>nivel[x])
    {
        if(nivel[y]-(1<<p)>=nivel[x])
            y=v[y][p];
        p--;
    }
    if(x==y)
        return x;
    for(int p=log;p>=0;p--)
    {
        if(v[x][p]!=v[y][p])
            x=v[x][p],y=v[y][p];
    }
    return v[x][0];
}
int main(){
    cin>>n>>q;
    while((1<<(log+1))<=n)
        log++;
    for(int i=2;i<=n;i++)
    {
        cin>>v[i][0];
        L[v[i][0]].push_back(i);
        L[i].push_back(v[i][0]);
    }

    dfs(1);
    int x,y ;
    while(q--)
    {
        cin>>x>>y;
        cout<<LCA(x,y)<<'\n';
    }
    return 0;
}