Cod sursa(job #2977296)

Utilizator aaagabiTurbinca Gabriel aaagabi Data 11 februarie 2023 11:41:56
Problema Lowest Common Ancestor Scor 100
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 1.16 kb
#include <bits/stdc++.h>

using namespace std;
ifstream fin("lca.in");
ofstream fout("lca.out");
int par[100005][19];
int tin[100005],tout[100005],timp,viz[100005];
vector <int> v[100005];
int n,m,x,y;

void dfs(int nod)
{
    tin[nod]=++timp;
    viz[nod]=1;
    for(int i=0;i<v[nod].size();i++)
        if(!viz[v[nod][i]])
        dfs(v[nod][i]);
    tout[nod]=++timp;
}
bool is_ancestor(int x,int y)
{
    if(x==0||x==y)
        return 1;
    if((tin[x]<tin[y]&&tout[x]>tout[y]))
        return 1;
    return 0;
}
int lca(int x,int y)
{
    if(is_ancestor(x,y))
       return x;
    if(is_ancestor(y,x))
        return y;
    for(int i=18;i>=0;i--)
    {
        if(!is_ancestor(par[x][i],y))
           x=par[x][i];
    }
    return par[x][0];
}
int main()
{
    fin>>n>>m;
    for(int i=2;i<=n;i++)
        {
            fin>>par[i][0];
            v[par[i][0]].push_back(i);
        }
    for(int j=1;j<=18;j++)
        for(int i=1;i<=n;i++)
        {
            par[i][j]=par[par[i][j-1]][j-1];
        }
    dfs(1);
    for(int i=1;i<=m;i++)
    {
        fin>>x>>y;
        fout<<lca(x,y)<<'\n';
    }
    return 0;
}