hdu4003/蓝桥杯 金属采集

思路：

树形dp + 分组背包dp。

参考https://www.cnblogs.com/kuangbin/archive/2012/08/29/2661928.html

实现：

 #include <bits/stdc++.h>
 using namespace std;
 typedef pair<int, int> pii;

 const int MAXN = ;
 vector<pii> G[MAXN];
 int dp[MAXN][], n, s, k;

 void dfs(int u, int f)
 {
     for (int i = ; i < G[u].size(); i++)
     {
         int v = G[u][i].first, w = G[u][i].second;
         if (v == f) continue;
         dfs(v, u);
         for (int j = k; j >= ; j--)
         {
             dp[u][j] += dp[v][] +  * w;
             for (int l = ; l <= j; l++)
             {
                 dp[u][j] = min(dp[u][j], dp[v][l] + l * w + dp[u][j - l]);
             }
         }
     }
 }

 int main()
 {
     while (scanf("%d %d %d", &n, &s, &k) != EOF)
     {
         memset(dp, , sizeof dp);
         for (int i = ; i <= n; i++) G[i].clear();
         int a, b, w;
         for (int i = ; i < n - ; i++)
         {
             scanf("%d %d %d", &a, &b, &w);
             G[a].push_back(pii(b, w));
             G[b].push_back(pii(a, w));
         }
         dfs(s, );
         printf("%d\n", dp[s][k]);
     }
     return ;
 }