HDU 1520（树形dp）

#pragma warning(disable:4996)
#include<cstdio>
#include<cstring>
#include<cmath>
#include<vector>
#include<algorithm>
#include<iostream>
using namespace std;

int father[6005];
int dp[6005][2];
int value[6005];
vector<int> list[6005];
int N, M;

void dfs(int father)
{
    int len = list[father].size();
    for(int i = 0; i <len; i++)
    {
        int child = list[father][i];
            dfs(child);
        dp[father][0]+= max(dp[child][0], dp[child][1]);
        dp[father][1] += dp[child][0];
    }
}
int main()
{
    //freopen("in.txt", "r", stdin);
    while (~scanf("%d", &N))
    {
        M++;
        memset(dp, 0, sizeof(dp));
        memset(value, 0, sizeof(value));
        for (int i = 1; i <= N; i++)
        {
            cin >> value[i];
            father[i] = -1;
            list[i].clear();
            dp[i][1] = value[i];
        }
        int a, b;
        while (cin >> a >> b, a || b)
        {
            father[a] = b;
            list[b].push_back(a);
        }
        int root = 1;
        while(father[root] != -1)
        {
            root = father[root];
        }
        dfs(root);
        cout << max(dp[root][0], dp[root][1]) << endl;
    }
    fclose(stdin);
    return 0;
}