hdu 5416 CRB and Tree（暴力）

题目链接：hdu 5416 CRB and Tree

dfs一遍，处理出每个位置到根的路径权值亦或和，W(u,v) = W(u,root)^W(v,root)，统计所有W(u,root)的情况数，对于每个询问值s，枚举u，ans 加上W(u,root)^s的情况数（Q值比较小）。注意s=0的情况。

#include <cstdio>
#include <cstring>
#include <vector>
#include <algorithm>

using namespace std;
typedef pair<int,int> pii;
typedef long long ll;
const int maxn = 1e6 + 5;

int N, Q, C[maxn], W[maxn];
vector<pii> G[maxn];

void dfs (int u, int f, int w) {
W[u] = w;
for (int i = 0; i < G[u].size(); i++) {
int v = G[u][i].first;
if (v == f) continue;
dfs(v, u, w ^ G[u][i].second);
}
}

void init () {
scanf("%d", &N);
memset(W, 0, sizeof(W));
memset(C, 0, sizeof(C));
for (int i = 1; i <= N; i++) G[i].clear();

int u, v, w;
for (int i = 1; i < N; i++) {
scanf("%d%d%d", &u, &v, &w);
G[u].push_back(make_pair(v, w));
G[v].push_back(make_pair(u, w));
}
dfs(1, 0, 0);
for (int i = 1; i <= N; i++) C[W[i]]++;
//C[0] += N;
}

int main () {
int cas, s;
scanf("%d", &cas);
while (cas--) {
init ();
scanf("%d", &Q);
for (int i = 0; i < Q; i++) {
ll ans = 0;
scanf("%d", &s);
for (int j = 1; j <= N; j++) {
int w = W[j] ^ s;
ans += C[w];
}
if (s == 0)
ans += N;
printf("%lld\n", ans / 2);
}
}
return 0;
}