hdu 1561 树形DP n个选m个价值最大

http://acm.hust.edu.cn/vjudge/problem/18068

#include <iostream>
#include <string>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <stack>
#include <queue>
#include <cctype>
#include <vector>
#include <iterator>
#include <set>
#include <map>
#include <sstream>
using namespace std;

#define mem(a,b) memset(a,b,sizeof(a))
#define pf printf
#define sf scanf
#define spf sprintf
#define pb push_back
#define debug printf("!
")
#define MAXN 500+5
#define MAX(a,b) a>b?a:b
#define blank pf("
")
#define LL long long
#define ALL(x) x.begin(),x.end()
#define INS(x) inserter(x,x.begin())
#define pqueue priority_queue
#define INF 0x3f3f3f3f

#define ls (rt<<1)
#define rs (rt<<1|1)

int n,m;

int head[MAXN],vis[MAXN],ptr=1;

int dp[MAXN][MAXN],num[MAXN],val[MAXN];

struct node{int y,next,val;}tree[MAXN<<2];

void init()
{
    mem(head,-1);
    mem(vis,0);
    mem(dp,0);
    ptr = 1;
}

void add(int son,int fa)
{
    tree[ptr].y=son;
    tree[ptr].next=head[fa];
    head[fa]=ptr++;
}

void dfs(int rt)
{
    num[rt] = vis[rt] = 1;
    dp[rt][1] = val[rt];
    for(int i = head[rt];i!=-1;i=tree[i].next)
    {
        int y = tree[i].y;
        if(vis[y]) continue;
        dfs(y);
        num[rt]+=num[y];
        for(int j = num[rt];j>1;j--)
        {
            for(int k = 1;k<j;k++)
            {
                dp[rt][j] = max(dp[rt][j],dp[rt][j-k]+dp[y][k]);
            }
        }
        //pf("rt%d y%d
",rt,y);
        //for(int j = 1;j<=num[rt];j++) pf("%d ",dp[rt][j]);
        //blank;
    }
}


int main()
{
    int i,j,k=1;
    while(~sf("%d%d",&n,&m) && m+n)
    {
        init();
        for(i=1;i<=n;i++)
        {
            int x,y;
            sf("%d%d",&x,&y);
            add(x,i);
            add(i,x);
            val[i] = y;
        }
        dfs(0);
        pf("%d
",dp[0][m+1]);
    }
}