HDU 1520 Anniversary party / 树形DP水题！！！

#include <cstdio>
#include <cstring>
#include <vector>
#include <algorithm>
using namespace std;
const int maxn = 6010;
vector <int> G[maxn];
double dp[maxn][2];
int a[maxn];
int in[maxn];
int n;

void dfs(int u)
{
	dp[u][1] = a[u];
	for(int i = 0; i < G[u].size(); i++)
	{
		int v = G[u][i];
		dfs(v);
		dp[u][0] += max(dp[v][0], dp[v][1]);
		dp[u][1] += dp[v][0];
	}
}
int main()
{
	int n;
	while(scanf("%d", &n) != EOF)	
	{
		for(int i = 1; i <= n; i++)
		{
			G[i].clear();
			in[i] = 0;
			scanf("%d", &a[i]);
		}
		int u, v;
		while(scanf("%d %d", &u, &v) && (u+v))
		{
			G[v].push_back(u);
			in[u]++;
		}
		memset(dp, 0, sizeof(dp));
		for(int i = 1; i <= n; i++)
		{
			if(!in[i])
			{
				dfs(i);
				//printf("%d\n", i);
				int ans = max(dp[i][0], dp[i][1]);
					printf("%d\n", ans);
				break;
			}
		}
	}
	return 0;
}