[HDU 1011] Starship Troopers (树形dp)

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1011

dp[u][i]为以u为根节点的，花了不超过i元钱能够得到的最大价值

因为题目里说要访问子节点必须先访问根节点，所以

dp[u][i+j] = max(dp[u][i],dp[u][i]+dp[v][j]); v是u的儿子节点。

代码：

 import java.util.*;
 import static java.lang.Math.*;

 class Graph{
     ArrayList<ArrayList<Integer>> e;
     int dp[][];
     boolean vis[];
     int n,m;
     public Graph(int n,int m){
         e = new ArrayList<ArrayList<Integer>>();
         for(int i=0;i<=n;i++){
             e.add(new ArrayList<Integer>());
         }
         dp = new int[n+1][m+1];
         vis = new boolean[n+1];
         this.n = n;
         this.m = m;
     }

     public void add_edge(int from,int to){
         ArrayList<Integer> t = e.get(from);
         t.add(to);
     }

     public int dfs(int u){
         if( vis[u] ) return 0;
         vis[u] = true;

         ArrayList<Integer> t = e.get(u);

         for(int i=m;i>=Main.w[u];i--) dp[u][i] = Main.v[u];

         for(int s:t ){
             if( vis[s] ) continue;
             dfs(s);

             for(int i=m;i>=Main.w[u];i--){
                 for(int j=1;j<=m;j++){
                     if( i+j<=m ){
                         dp[u][i+j] =max(dp[u][i+j], dp[u][i]+dp[s][j]);
                     }
                 }
             }
         }
         return dp[u][m];
     }

 }

 public class Main{
     static int N,M;
     static Scanner sc = new Scanner(System.in);
     static int w[],v[];
     public static void main(String[] args){
         while( sc.hasNext() ){

             N = sc.nextInt();
             M = sc.nextInt();

             if( N==-1 && M==-1 ) break;

             w = new int[N+1];
             v = new int[N+1];

             Graph g = new Graph(N,M);

             for(int i=1;i<=N;i++){
                 w[i] = sc.nextInt();
                 v[i] = sc.nextInt();
                 w[i] = (w[i]+19)/20;
             }

             for(int i=1;i<N;i++){
                 int a = sc.nextInt();
                 int b = sc.nextInt();
                 g.add_edge(a,b);
                 g.add_edge(b,a);
             }

             if( M==0 ){
                 System.out.println(0);
                 continue;
             }

             int ans = g.dfs(1);
             System.out.println(ans);

         }

     }

 }