LCA Err

#include <iostream>
#include <vector>
using namespace std;

const int MAXN=2e5+6;

struct node
{
    int val, pos;
    node(int _val=0, int _pos=0) { val=_val; pos=_pos;}
};

node t[1000006];

int n,T,s;
std::vector<int> E;
std::vector<int> Level;
int P[MAXN];

vector<int> a[MAXN];

void DFS(int u, int par,int lvl)
{
    E.push_back(u);
    Level.push_back(lvl);

    for(int v: a[u])
        if (v!=par)
        {
            DFS(v,u,lvl+1);
            E.push_back(u);
            Level.push_back(lvl);

        }
}

node Combine(node a, node b)
{
    if (a.val>b.val) return b;
    return a;
}

void Build(int id, int l, int r)
{
    if (l==r)
    {
        t[id]=node(Level[l-1],l);
        return;
    }
    int mid=(l+r)>>1;
    Build(id*2,l,mid);
    Build(id*2+1,mid+1,r);
    t[id]=Combine(t[id*2],t[id*2+1]);
}

node Query(int id, int l, int r, int L, int R)
{
    if (r<L || R<l) {return node(999999,-1);}
    if (L<=l && r<=R)
    {
        return t[id];
    }
    int mid=(l+r)>>1;
    return Combine(Query(id*2,l,mid,L,R), Query(id*2+1,mid+1,r,L,R));
}

int main(int argc, char const *argv[])
{
    // freopen("input.txt","r",stdin);
    cin >>n  >> T;

    int u,v;
    for (int i = 2; i <= (n); ++i)
    {
        cin >> u;
        a[u].push_back(i);
    }

    DFS(1,1,1);
    for(int i=0; i<(int)E.size(); i++)
    {
        if (!P[E[i]]) P[E[i]]=i+1;
    }

    s=E.size();
    Build(1,1,s);

    while (T--)
    {
        cin >> u >> v;
        node tmp=Query(1,1,s,min(P[u],P[v]),max(P[u],P[v]));
        cout<<E[tmp.pos-1]<<endl;
    }