Hdu 1520 Anniversary party (树形dp入门，类似最大独立集)

#include <cstdio>
#include <vector>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
const int maxn = 6100;
vector<int> G[maxn];
int d[maxn][2],c[maxn];
/*
1 该节点已经选取
0 该节点未选区
*/
bool vis[maxn][2];
int dp(int i,int j,int f){
   if(vis[i][j]) return d[i][j];
   vis[i][j] =true;
   if(G[i].size()==1&&G[i][0]==f){
       return d[i][j] = 0;
   }
   d[i][j]=0;
   for(int k=0;k<G[i].size();k++){
      if(G[i][k]==f) continue;
      if(j&1) d[i][j]+=dp(G[i][k],0,i);
      else    d[i][j]+=max(dp(G[i][k],0,i),dp(G[i][k],1,i)+c[G[i][k]]);
   }
   return d[i][j];
}
int main()
{
    int n;
         while(scanf("%d",&n)==1){
          for(int i=1;i<=n;i++){
              G[i].clear();
              scanf("%d",&c[i]);
          }
          for(int i=1;i<=n;i++){
              int x,y;
              scanf("%d %d",&x,&y);
              if(!x||!y) break;
              G[x].push_back(y);
              G[y].push_back(x);
          }
          memset(vis,false,sizeof(vis));
          printf("%d\n",max(dp(1,0,-1),dp(1,1,-1)+c[1]));
         }
    return 0;
}