一本通1557：祖孙询问

#include <bits/stdc++.h>
const int NN = 4e4 + 4;
using namespace std;
vector<int> G[NN];
int N, TI[NN], TO[NN], timer = 0;
void dfs(int u, int fa = -1) {
    TI[u] = ++timer;

    for (int v : G[u])
        if (v != fa)
            dfs(v, u);

    TO[u] = ++timer;
}
bool isAncestor(int u, int v) {
    return TI[u] < TI[v] && TO[v] < TO[u];
}
int solve(int u, int v) {
    if (isAncestor(u, v))
        return 1;

    if (isAncestor(v, u))
        return 2;

    return 0;
}
int main() {
    ios::sync_with_stdio(false), cin.tie(0);
    int N, M, root;
    cin >> N;

    for (int i = 1, u, v; i <= N; i++) {
        cin >> u >> v;

        if (v == -1)
            root = u;
        else
            G[u].push_back(v), G[v].push_back(u);
    }

    dfs(root);
    cin >> M;

    for (int i = 1, u, v; i <= M; i++)
        cin >> u >> v, printf("%d\n", solve(u, v));

    return 0;
}