hdu 1561 The more, The Better

http://acm.hdu.edu.cn/showproblem.php?pid=1561

同hdu1011只是这里做的小处理是将0点加入，将原来的森林变成了树，这样就可以按照树形dp展开来做了。。

dp[i][j]表示从i点往后占领j个城市所获得的总的最多宝物

dp[i][j]=max(dp[i][j],dp[i][j-k]+dp[son[i]][k])

#include <cstdio>
#include <iostream>
#include <algorithm>
#include <vector>
#include <cstring>
#define maxn 207
using namespace std;
int val[maxn],visit[maxn],dp[maxn][maxn];
vector<int>g[maxn];
int n,m;
void dfs(int pos)
{
    int i,j;
    visit[pos] = true;
    for (i = 1; i <= m; ++i)
    {
       dp[pos][i] =  val[pos];
    }
    for (i = 0; i < g[pos].size(); ++i)
    {
        int p = g[pos][i];
        if(visit[p])
        continue;
        dfs(p);
        for (j = m; j >= ( pos==0 ? 0:1); --j)
        {
            for (int k = 1; j + k <= m; ++k)
            if(dp[p][k])
            dp[pos][j+k] = max(dp[pos][j+k],dp[pos][j]+dp[p][k]);
        }
    }

}
int main()
{
    //freopen("d.txt","r",stdin);
    int i,a;
    while(scanf("%d%d",&n,&m))
    {
        memset(val,0,sizeof(val));
        if(!n&&!m) break;
        for (i = 0; i <= n; ++i)
        g[i].clear();
        for (i = 1; i <= n; ++i)
        {
            scanf("%d%d",&a,&val[i]);
            g[a].push_back(i);//有向图
        }
        memset(dp,0,sizeof(dp));
        memset(visit,false,sizeof(visit));
        dfs(0);
        printf("%d\n",dp[0][m]);
    }
    return 0;
}