Cod sursa(job #2974130)

Utilizator alessiamtr12Mitrica Alessia alessiamtr12 Data 3 februarie 2023 11:28:06
Problema Lowest Common Ancestor Scor 100
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 1.2 kb
#include <fstream>
#include<vector>
#define NMAX 100001
using namespace std;
ifstream fin("lca.in");
ofstream fout("lca.out");
int n,m,q,x,y;
int nivel[NMAX],tata[20][NMAX];
vector<int>v[NMAX];
void dfs(int nod,int niv)
{
    nivel[nod]=niv;
    for(int i=0;i<v[nod].size();i++)
    {
        int nod1=v[nod][i];
        dfs(nod1,niv+1);
    }
}
int lca(int x,int y)
{
    if(nivel[x]<nivel[y])
        swap(x,y);

    int log1,log2;
    for(log1=1; (1<<log1)<nivel[x]; log1++);
    for(log2=1; (1<<log2)<nivel[y]; log2++);

    for(int k=log1;k>=0;k--)
       if(nivel[x]-(1<<k)>=nivel[y])
          x=tata[k][x];
    if(x==y)
        return x;

	for(int k=log2;k>=0;k--)
		if(tata[k][x]&&tata[k][x]!=tata[k][y])
			{
			    x=tata[k][x];
		     	y=tata[k][y];
			}

	return tata[0][x];

}
int main()
{
    fin>>n>>q;
    for(int i=2;i<=n;i++)
        {
            fin>>tata[0][i];
            v[tata[0][i]].push_back(i);
        }
    for(int k=1;(1<<k)<=n;k++)
          for(int i=1;i<=n;i++)
              tata[k][i]=tata[k-1][tata[k-1][i]];
    dfs(1,0);

    for(int i=1;i<=q;i++)
    {
        fin>>x>>y;
        fout<<lca(x,y)<<"\n";
    }
    return 0;
}