HDU1520——树形DP——Anniversary party

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<vector>
using namespace std;
int dp[6100][2];
int t[6100];
int f[6100];
vector<int> G[6100];
void dfs(int x)
{
    dp[x][1] = t[x];
    for(int i = 0; i < G[x].size(); i++){
        dfs(G[x][i]);
    }
    for(int i = 0 ; i < G[x].size();i++){
        dp[x][1] += dp[G[x][i]][0];
        dp[x][0] += max(dp[G[x][i]][1],dp[G[x][i]][0]);
    }
}

int main()
{
    int n,a,b;
    while(~scanf("%d",&n)){
        for(int i = 1; i <= n; i++)
            G[i].clear();
        for(int i = 1; i <= n ; i++)
            scanf("%d",&t[i]);
        memset(f,-1,sizeof(f));
        memset(dp,0,sizeof(dp));
        while(~scanf("%d%d",&a,&b)){
                if(a == 0 && b == 0) break;
            G[b].push_back(a);
            f[a] = b;
        }
       // for(int i = 1;  i<= n ;i++)
       //     printf("%d ",f[i]);
        int x = 1;
        while(f[x]!= -1) {
            x = f[x];
        }
        dfs(x);
    printf("%d\n",max(dp[x][0],dp[x][1]));
    }
    return 0;
}