[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);
            
        }
        
    }
    
    
}