参考答案：

#include<iostream>
#include<queue>
#include<cstring>
using namespace std;
const int N = 40010 * 2, M = 17;
int e[N], ne[N], h[N], idx;
int f[N][M];
int depth[N];
int st[N];
int n, m;
queue<int> q;
void add(int a, int b)
{
    e[idx] = b, ne[idx] = h[a], h[a] = idx++;
}
void bfs(int root)
{
    depth[0] = 0, depth[root] = 1;
    q.push(root);
    st[root] = 1;
    while (q.size())
    {
        int t = q.front();
        q.pop();
        for (int i = h[t]; ~i; i = ne[i])
        {
            int j = e[i];
            if (!st[j])
            {
                depth[j] = depth[t] + 1;
                f[j][0] = t;
                for (int k = 1; k <= 16; ++k)
                {
                    f[j][k] = f[f[j][k - 1]][k - 1];
                }
                q.push(j);
                st[j] = 1;
            }
        }
    }
}
int lca(int a, int b)
{
    if (depth[a] < depth[b]) swap(a, b);
    for (int k = 16; k >= 0; --k)
    {
        if (depth[f[a][k]] >= depth[b]) a = f[a][k];
    }
    if (a == b) return a;
    for (int k = 16; k >= 0; --k)
    {
        if (f[a][k] != f[b][k])
        {
            a = f[a][k];
            b = f[b][k];
        }
    }
    return f[a][0];
}
int main()
{
    memset(h, -1, sizeof(h));
    cin >> n;
    int root = 0;
    for (int i = 0; i < n; ++i)
    {
        int a, b;
        cin >> a >> b;
        if (b == -1)
        {
            root = a;
            continue;
        }
        add(a, b);
        add(b, a);
    }

    bfs(root);
    cin >> m;
    for (int i = 0; i < m; ++i)
    {
        int x, y;
        cin >> x >> y;
        int p = lca(x, y);
        if (p == x) puts("1");
        else if (p == y) puts("2");
        else puts("0");
    }
    return 0;
}