hdu 1520 树形dp

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1520

#include<cstdio>
#include<cstring>
#include<cmath>
#include<iostream>
#include<algorithm>
#include<queue>
#include<vector>
using namespace std;
const int maxn = 6050;
const int maxe = 10000;
const int INF = 0x3f3f3f;

struct Edge{
    int u,v;
    int next;
    void assign(int u_,int v_,int next_){
        u = u_;    v = v_;   next = next_;
    }
}tree[maxe];

int head[maxn];
int dp[maxn][2];
int R[maxn];
int vis[maxn];
int cnt;
int N,M;

void addedge(int u,int v){
    tree[cnt].assign(u,v,head[u]);
    head[u] = cnt++;
}
void init(){
    cnt = 0;
    memset(dp,0,sizeof(dp));
    memset(head,-1,sizeof(head));
    memset(vis,0,sizeof(vis));
}

void dfs(int u,int fa){
    dp[u][1] = R[u];
    for(int i=head[u];i!=-1;i=tree[i].next){
        int v = tree[i].v;
        if(v == fa) continue;
        dfs(v,u);
        dp[u][1] += dp[v][0];
        dp[u][0] += max(dp[v][1],dp[v][0]);
    }
}
int main()
{
    //freopen("E:\\acm\\input.txt","r",stdin);

    while(cin>>N){
        init();
        for(int i=1;i<=N;i++)    scanf("%d",&R[i]);
        int u,v;
        while(scanf("%d%d",&v,&u) && u+v){
            addedge(u,v);
            vis[v] = true;
        }
        int root;
        for(int i=1;i<=N;i++)    if(!vis[i])  { root = i; break; }
        memset(vis,0,sizeof(vis));
        dfs(root,-1);
        printf("%d\n",max(dp[root][1],dp[root][0]));
    }

}