树形dp入门

#include<iostream>
#include<string.h>
#include<stdio.h>
#include<vector>
using namespace std;
const int maxa = 6005;
int n;
vector< int> xiashu[maxa];
int dp[maxa][2];
int v[maxa];
int du[maxa];
int dfs(int x, int zai){
    int maxn = 0;
    int sum = 0;
    if(dp[x][zai])
        return dp[x][zai];
    for(int i = 0;i < xiashu[x].size(); i++){
        int k = xiashu[x][i];
        sum += dfs(k, 0);
    }
    maxn = sum;
    if(zai)
        return dp[x][zai] = maxn;
    sum = 0;
    for(int i = 0; i < xiashu[x].size(); i++){
        int k = xiashu[x][i];
        sum += dfs(k, 1);
    }
    return dp[x][zai] = max(maxn, sum +v[x]);
}
int main(){
    while(scanf("%d", &n)!=EOF){
        for(int i = 1;i  <= n; i++){
            scanf("%d", &v[i]);
        }
        memset(dp, 0, sizeof(dp));
        memset(du, 0, sizeof(du));
        for(int i = 1; i<= n; i++)
            xiashu[i].clear();
        int x, y;
        while(1){
            scanf("%d%d", &x, &y);
            if(!y && !x)
                break;
            xiashu[y].push_back(x);
            du[x]++;
        }
        for(int i = 1; i <= n; i++){
            if(du[i]==0)
                printf("%d\n", dfs(i, 0));
        }
    }
}