POJ 2342Anniversary party（树形DP）

#pragma warning(disable:4996)#include <cstdio>#include <iostream>#include <cstring>#include <vector>#include <algorithm>#define N 6005using namespace std;//树形dp：通过“所有”子节点的信息来更新父节点的信息//g[u]里面放着u的所有儿子vector<int>g[N];//dp[i][0]表示第i个人不参加聚会得到的最大值，dp[i][1]表示第i个人参加聚会能得到的最大值//转移方程是：dp[i][0]+=max(dp[son][1],dp[son][0]) 初始化时dp[i][0]为0//           dp[i][1]+=dp[son][0]  初始化dp[i][1]为a[i]//借助vis数组来找到rootint vis[N], dp[N][2], a[N];void dfs(int u){dp[u][1] = a[u];dp[u][0] = 0;for (int i = 0; i < g[u].size(); i++){int v = g[u][i];dfs(v);dp[u][0] += max(dp[v][1], dp[v][0]);dp[u][1] += dp[v][0];}}int main(){int n;while (scanf("%d", &n) != EOF){if (n == 0){scanf("%d", &n);break;}memset(dp, 0, sizeof dp);for (int i = 0; i <= n; i++){g[i].clear();vis[i] = false;}for (int i = 1; i <= n; i++)scanf("%d", a + i);for (int i = 1; i < n; i++){int u, v; scanf("%d %d", &u, &v);g[v].push_back(u);vis[u] = true;}int root = 0;for (int i = 1; i <= n; i++){if (vis[i] == false){root = i;break;}}dfs(root);printf("%d\n", max(dp[root][0], dp[root][1]));}return 0;}