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Cod sursa(job #801047)
#include <fstream>
using namespace std;
ifstream in("lca.in");
ofstream out("lca.out");
const int N=250005,lg=19;
int t[N][lg],depth[N];
int bs(int x, int y)
{
int i;
for(i=lg-1;i>=0;i--)
if(x>=(1<<i))
{
x-=(1<<i);
y=t[i][y];
}
return y;
}
void dfs(int i)
{
if (!t[0][i]){
depth[i] = 1;
return;
}
if (!depth[ t[0][i] ])
dfs(t[0][i]);
depth[i]=depth[t[0][i]]+1;
}
int rez(int x,int y)
{
for(int i=lg;i>=0;i--)
if(t[i][x]!=t[i][y])
{
x=t[i][x];
y=t[i][y];
}
return t[0][x];
}
int main()
{
int n,m,i,x,y;
in>>n>>m;
for(i=2;i<=n;i++)
in>>t[0][i];
for(i=1;i<lg;i++)
for(int j=1;j<=n;j++)
t[i][j]=t[i-1][t[i-1][j]];
for(i=1;i<=n;i++)
{
if(!depth[i])
dfs(i);
}
while(m--)
{
in>>x>>y;
if(depth[x]>depth[y])
x=bs(depth[x]-depth[y],x);
else
y=bs(depth[y]-depth[x],y);
out<<rez(x,y)<<"\n";
}
}