描述
You're given a tree with weights of each node, you need to find the maximum subtree of specified size of this tree.
Tree Definition
A tree is a connected graph which contains no cycles.
输入
There are several test cases in the input.
The first line of each case are two integers N(1 <= N <= 100), K(1 <= K <= N), where N is the number of nodes of this tree, and K is the subtree's size, followed by a line with N nonnegative integers, where the k-th integer indicates the weight of k-th node. The following N - 1 lines describe the tree, each line are two integers which means there is an edge between these two nodes. All indices above are zero-base and it is guaranteed that the description of the tree is correct.
输出
One line with a single integer for each case, which is the total weights of the maximum subtree.
样例输入
3 1
10 20 30
0 1
0 2
3 2
10 20 30
0 1
0 2
样例输出
30
40
题目大意:给定一颗树,求结点数为k的子树的最大权值。
解题思路:树形dp,dp[i][j]表示以第i个结点为根,有j个结点的子树的最大权值。
#include <bits/stdc++.h> using namespace std; #define LL long long const int N=105; vector<int>G[N]; int dp[N][N],m,d[N],a[N]; void dfs(int u) { dp[u][1]=a[u]; for(int i=0;i<G[u].size();i++){ int v=G[u][i]; dfs(v); for(int j=m;j>=1;j--){ for(int k=1;k<=j;k++){ if(j-k>=0) dp[u][j]=max(dp[u][j],dp[u][k]+dp[v][j-k]); } } } } int main() { int n; while(cin>>n>>m){ for(int i=0;i<=n;i++){ G[i].clear();d[i]=0; for(int j=0;j<=m;j++) dp[i][j]=0; } for(int i=0;i<n;i++) cin>>a[i]; for(int i=1,u,v;i<n;i++){ cin>>u>>v; G[u].push_back(v); d[v]++; } int pos=-1; for(int i=0;i<n;i++) if(d[i]==0) dfs(i); int ans=-1; for(int i=0;i<n;i++) ans=max(ans,dp[i][m]); cout<<ans<<endl; } }