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Cod sursa(job #608145)
#include <fstream>
using namespace std;
int n,m,a[100001],x,y,i,j,p[100001][20],l[100001];
int lca(int n,int p[100001][20],int a[100001],int l[100001],int x,int y)
{
int i,t,lg;
if(l[x]<l[y])
t=x,x=y,y=t;
for(lg=1;(1<<lg)<=l[x];lg++);
--lg;
for(i=lg;i>=0;--i)
if(l[x]-(1<<i)>=l[y])
x=p[x][i];
if(x==y)
return x;
for(i=lg;i>=0;--i)
if(p[x][i]!=-1&&p[x][i]!=p[y][i]&&p[y][i]!=-1)
x=p[x][i],y=p[y][i];
return a[x];
}
int main()
{
ifstream fin("lca.in");
ofstream fout("lca.out");
fin>>n>>m;
l[1]=1;
for(i=2;i<=n;++i)
{
fin>>a[i];
l[i]=l[a[i]]+1;
}
for(i=0;i<=n;++i)
for(j=1;j<=18;++j)
p[i][j]=-1;
for(i=1;i<=n;++i)
p[i][0]=a[i];
for(j=1;j<=18;++j)
for(i=0;i<=n;++i)
if(p[i][j-1]!=-1)
p[i][j]=p[p[i][j-1]][j-1];
for(;m;--m)
{
fin>>x>>y;
fout<<lca(n,p,a,l,x,y)<<"\n";
}
return 0;
}