用C++

以下是使用 C++ 实现的代码：

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

#define MAXN 50000
#define MAXM 500000
#define MAXLOGN 16

int n, m;
int fa[MAXN][MAXLOGN], dep[MAXN];
int head[MAXN], to[MAXM << 1], nxt[MAXM << 1], tot;

void add_edge(int u, int v) {
    to[++tot] = v;
    nxt[tot] = head[u];
    head[u] = tot;
}

void dfs(int u, int f, int d) {
    fa[u][0] = f;
    dep[u] = d;
    for (int i = 1; i < MAXLOGN; i++) {
        fa[u][i] = fa[fa[u][i - 1]][i - 1];
    }
    for (int i = head[u]; i; i = nxt[i]) {
        int v = to[i];
        if (v != f) {
            dfs(v, u, d + 1);
        }
    }
}

int lca(int u, int v) {
    if (dep[u] < dep[v]) {
        int tmp = u;
        u = v;
        v = tmp;
    }
    for (int i = MAXLOGN - 1; i >= 0; i--) {
        if (dep[fa[u][i]] >= dep[v]) {
            u = fa[u][i];
        }
    }
    if (u == v) {
        return u;
    }
    for (int i = MAXLOGN - 1; i >= 0; i--) {
        if (fa[u][i] != fa[v][i]) {
            u = fa[u][i];
            v = fa[v][i];
        }
    }
    return fa[u][0];
}

int main() {
    while (scanf("%d", &n) && n) {
        memset(head, 0, sizeof(head));
        tot = 0;
        for (int i = 1; i < n; i++) {
            int u, v;
            scanf("%d%d", &u, &v);
            add_edge(u, v);
            add_edge(v, u);
        }
        dfs(0, 0, 0);
        scanf("%d", &m);
        while (m--) {
            int a, b, c;
            scanf("%d%d%d", &a, &b, &c);
            int ab = lca(a, b);
            int ac = lca(a, c);
            int bc = lca(b, c);
            if ((ab == ac && lca(c, b) == b) || (ab == bc && lca(c, a) == a)) {
                printf("Yes\n");
            } else {
                printf("No\n");
            }
        }
    }
    return 0;
}

同样地，上面的代码假设输入的节点编号从 $0$ 到 $n-1$，如果从 $1$ 到 $n$，需要将输入的节点编号减一。