HDU5416(树DP)

比较水，坑点是答案要爆int。

#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;
#define maxn 511111
#define maxm 1111111
#define INF 111111111

struct node {
    int from, to, next, w;
}edge[maxm];
int head[maxn], sum[maxn]; //异或和
int cnt[maxn];
int e, n;

void add_edge (int from, int to, int w, int i) {
    node &e = edge[i];
    e.from = from, e.to = to, e.w = w, e.next = head[from], head[from] = i;
}

void dfs (int u, int fa) {
    for (int i = head[u]; i != -1; i = edge[i].next) {
        int v = edge[i].to;
        if (v == fa)
            continue;
        sum[v] = sum[u]^edge[i].w;
        dfs (v, u);
    }
}

int main () {
    int t;
    scanf ("%d", &t);
    while (t--) {
        scanf ("%d", &n);
        memset (cnt, 0, sizeof cnt);
        memset (head, -1, sizeof head);
        e = 0;
        int u, v, w;
        for (int i = 1; i < n; i++) {
            scanf ("%d%d%d", &u, &v, &w);
            add_edge (u, v, w, e++);
            add_edge (v, u, w, e++);
        }
        memset (sum, 0, sizeof sum);
        dfs (1, 0);
        for (int i = 1; i <= n; i++) {
            cnt[sum[i]]++;
        }
        //for (int i = 1; i <= n; i++) cout << sum[i] << " "; cout <<endl;
        int q;
        scanf ("%d", &q);
        while (q--) {
            scanf ("%d", &w);
            long long ans = 0;
            for (int i = 1; i <= n; i++) {
                int gg = w^sum[i];
                if (sum[i] == gg)
                    ans++;
                ans += cnt[gg];
            }
            printf ("%lld\n", ans/2);
        }
    }
    return 0;
}