点的距离

#include <iostream>
#include <cstdio>
#include <string>
using namespace std;
int dfn[500001], f[500001][21];
int n, m, cnt, root;
int head[500001], lg[500001];
struct tu {
    int v, nxt;
} e[5000001];
void add(int u, int v) {
    e[++cnt].v = v;
    e[cnt].nxt = head[u];
    head[u] = cnt;
}
void dfs(int now, int fa) {
    dfn[now] = dfn[fa] + 1;
    f[now][0] = fa;
    for (int i = 1; (1 << i) <= dfn[now]; i++) f[now][i] = f[f[now][i - 1]][i - 1];
    for (int i = head[now]; i; i = e[i].nxt) {
        if (e[i].v != fa)
            dfs(e[i].v, now);
    }
}
int lca(int x, int y) {
    if (dfn[x] < dfn[y])
        swap(x, y);
    while (dfn[x] > dfn[y]) {
        x = f[x][lg[dfn[x] - dfn[y]]];
    }
    if (x == y)
        return x;
    for (int k = lg[dfn[x]]; k >= 0; k--)
        if (f[x][k] != f[y][k])
            x = f[x][k], y = f[y][k];
    return f[x][0];
}
int main() {
    scanf("%d", &n);
    for (int i = 1; i <= n - 1; i++) {
        int x, y;
        scanf("%d%d", &x, &y);
        add(x, y);
        add(y, x);
    }
    dfs(1, 0);
    lg[0] = -1;
    for (int i = 1; i <= n; i++) lg[i] = lg[i >> 1] + 1;  //求log+1
    // for(int i=1;i<=n;i++)
    // printf("%d ",lg[i]);
    scanf("%d", &m);
    for (int i = 1; i <= m; i++) {
        int x, y;
        scanf("%d%d", &x, &y);
        int mm = dfn[lca(x, y)];
        printf("%d
", dfn[x] - mm + dfn[y] - mm);
    }
    return 0;
}