HDU 1561（The more, The Better）

#include <iostream>
#include <algorithm>
using namespace std;
const int MAXN = 205;

struct Edge //邊
{
    int to; //到達結點
    int next; //出發結點的下一條邊的編號
}edge[MAXN];

int dp[MAXN][MAXN]; //動態規劃數組
int head[MAXN]; //head[i]表示從結點i出發的第1條邊的編號
int val[MAXN]; //結點的價值
int total; //邊的總數

//添加結點u到結點v的邊
void addEdge(int u, int v)
{
    edge[++total].to = v;
    edge[total].next = head[u];
    head[u] = total;
}

//深搜，搜索以結點u爲根結點，選取num個結點的最大價值
void DFS(int u, int num)
{
    if (num <= 0) 
        return;

    for (int i = head[u]; i != -1; i = edge[i].next)
    {
        int v = edge[i].to;
        DFS(v, num - 1);
        for (int j = num; j > 1; j--)
        {
            for (int k = 1; k <= num - 1; k++)
            {
                if (j > k)
                    dp[u][j] = max(dp[u][j], dp[u][j - k] + dp[v][k]);
            }
        }
    }
}

int main()
{
    int N, M;
    while (cin >> N >> M)
    {
        if (N == 0 && M == 0)
            break;

        memset(dp, -1, sizeof(dp));
        memset(head, -1, sizeof(head));
        total = 0;

        int a, b;
        for (int i = 1; i <= N; i++)
        {
            cin >> a >> b;
            addEdge(a, i);
            val[i] = b;
            dp[i][1] = val[i];
        }

        dp[0][1] = 0; //令整棵樹的根結點編號爲0，價值爲0
        ++M;
        DFS(0, M);
        cout << dp[0][M] << endl;
    }
    return 0;
}