HDU 1520 Anniversary party 树形dp

状态转移方程：

dp[u][0] = max(dp[v][0],dp[v][1]);

dp[u][1] += dp[v][0];

#include <iostream>
#include <cstdio>
#include <vector>
#include <cstring>
#include <algorithm>
using namespace std;
const int maxn = 6010;
vector<int>tree[maxn];

int rat[maxn],deg[maxn],dp[maxn][2];
int max(int x,int y){
    return x > y ? x : y;
}
void dfs(int u){
    if(0 == tree[u].size())
    {
        dp[u][1] = rat[u];
        return ;
    }
    dp[u][1] += rat[u];
    for(int i = 0; i < tree[u].size(); i++){
        int v = tree[u][i];
        dfs(v);
        dp[u][0] += max(dp[v][0],dp[v][1]);
        dp[u][1] += dp[v][0];
    }
}
int main()
{
   // freopen("in.txt","r",stdin);
    int n,l,k,root;
    while( ~scanf("%d",&n) ){
        for( int i = 1; i <= n; i++){
            tree[i].clear();
            scanf("%d",rat+i);
        }
        memset(deg,0,sizeof(deg));
        while( ~scanf("%d%d",&l,&k) , l||k){
            deg[l]++;
            tree[k].push_back(l);
        }
        memset(dp,0,sizeof(dp));
        for( root = 1; root <= n; root ++){
            if( !deg[root]){
                dfs(root);
                break;
            }
        }
        printf("%d
",max(dp[root][0],dp[root][1]));
    }
    return 0;
}