Binary Apple Tree URAL - 1018 [简单树形dp]

1018. Binary Apple Tree

Time limit: 1.0 second
Memory limit: 64 MB

Let's imagine how apple tree looks in binary computer world. You're right, it looks just like a binary tree, i.e. any biparous branch splits up to exactly two new branches. We will enumerate by integers the root of binary apple tree, points of branching and the ends of twigs. This way we may distinguish different branches by their ending points. We will assume that root of tree always is numbered by 1 and all numbers used for enumerating are numbered in range from 1 to  N, where  N is the total number of all enumerated points. For instance in the picture below  N is equal to 5. Here is an example of an enumerated tree with four branches:

2 5 \ / 3 4 \ / 1

As you may know it's not convenient to pick an apples from a tree when there are too much of branches. That's why some of them should be removed from a tree. But you are interested in removing branches in the way of minimal loss of apples. So your are given amounts of apples on a branches and amount of branches that should be preserved. Your task is to determine how many apples can remain on a tree after removing of excessive branches.

Input

First line of input contains two numbers:  N and  Q (2 ≤  N ≤ 100; 1 ≤  Q ≤  N − 1).  N denotes the number of enumerated points in a tree.  Q denotes amount of branches that should be preserved. Next  N − 1 lines contains descriptions of branches. Each description consists of a three integer numbers divided by spaces. The first two of them define branch by it's ending points. The third number defines the number of apples on this branch. You may assume that no branch contains more than 30000 apples.

Output

Output should contain the only number — amount of apples that can be preserved. And don't forget to preserve tree's root ;-)

Sample

input	output
5 2 1 3 1 1 4 10 2 3 20 3 5 20	21

Problem Source: Ural State University Internal Contest '99 #2 

Tags:  dynamic programming   ( hide tags for unsolved problems)

Difficulty: 289     Printable version      Submit solution      Discussion (83)

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题目：一棵有n个节点的树，去掉一些边，使得剩下q条边，边权和最大，1为根节点，必须保留。

分析：

//q条边就是q+1个点，dp[u][i] 表示以u为根的子树里选一个大小是i的包含根的连通块的最大权值;
//转移枚举两个儿子的size合并上来，复杂度n^2

代码：

#include
#define ll long long


//q条边就是q+1个点，dp[u][i] 表示以u为根的子树里选一个大小是i的包含根的连通块的最大权值;
//转移枚举两个儿子的size合并上来，复杂度n^2

using namespace std;
const int maxn = 130;
int n, q, tot, head[maxn], dp[maxn][maxn], vsize[maxn];

struct node{
    int next, to, val;
    node() {};
    node(int _next, int _to, int _val) : next(_next), to(_to), val(_val) {}
} edge[10*maxn*maxn];

void add(int u, int v, int w)
{
    edge[tot] = node(head[u], v, w);
    head[u] = tot++;
}

void dfs(int u, int fa)
{
    vsize[u] = 1;
    for(int i = head[u]; i != -1; i = edge[i].next)
    {
        int v = edge[i].to;
        if(v == fa) continue;
        dfs(v, u);
        vsize[u] += vsize[v];
    }
    for(int i = head[u]; i != -1; i = edge[i].next)
    {
        int v = edge[i].to;
        if(v == fa) continue;
        for(int j = vsize[u]; j > 1; j--)
        {
            for(int k = 1; k