Cod sursa(job #2654645)

Utilizator Gliumarin negai Gliu Data 1 octombrie 2020 20:08:26
Problema Lowest Common Ancestor Scor 20
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 1.04 kb
#include <fstream>
#include <vector>
#include <cmath>
using namespace std;
ifstream cin("lca.in");
ofstream cout("lca.out");
int n,m,x,y,jmp[100005][50],Lev[100005];
vector<int>v[100005];
int dfs(int nod,int lev){
	Lev[nod]=Lev[lev]+1;
    jmp[nod][0]=lev;
	for(int i=1;i<log(n);i++)
	  jmp[nod][i]=jmp[jmp[nod][i-1]][i-1];
	       
	for(int i=0;i<v[nod].size();i++){
		int s=v[nod][i];
		if(s==lev)continue;
		  dfs(s,nod);
	}	    
}
int lca(int x,int y){
	if(Lev[x]<Lev[y])
	      swap(x,y);
	int diff=Lev[x]-Lev[y];
	for(int k=20;k>=0;k--)
		if(diff>=(1<<k)){
			x=jmp[x][k];
			diff-=1<<k;
		}
	if(x==y)return x;
	
	for(int k=20;k>=0;k--){
		int x1,y1;
		x1=jmp[x][k];
		y1=jmp[y][k];
		if(x1 !=y1){
			x=x1;y=y1;
		}
	}
	return jmp[x][0];
	
}

int main(){
cin >>n>>m;
for(int i=2;i<=n;i++){
cin>>jmp[0][i];	
v[jmp[0][i]].push_back(i);
}
dfs(1,0);
for(int i=1;i<=n;i++)
	for(int k=1;(1<<k)<=n;k++)
		jmp[i][k]=jmp[jmp[i][k-1]][k-1];
	
while(m--){
	cin >>x>>y;
	cout <<lca(x,y)<<"\n";
}
return 0;
}