Rebuilding Roads Time Limit: 1000MS   Memory Limit: 30000K Total Submissions: 11495   Accepted: 5276 Description The cows have reconstructed Farmer John's farm, with its N barns (1 <= N <= 150, number 1..N) after the terrible earthquake last May. Th…

Rebuilding RoadsTime Limit: 1000MS Memory Limit: 30000KTotal Submissions: 8589 Accepted: 3854Description The cows have reconstructed Farmer John's farm, with its N barns (1 <= N <= 150, number 1..N) after the terrible earthquake last May. The cows d…

Description The cows have reconstructed Farmer John's farm, with its N barns (1 <= N <= 150, number 1..N) after the terrible earthquake last May. The cows didn't have time to rebuild any extra roads, so now there is exactly one way to get from any g…

题目大概是给一棵树,问最少删几条边可以出现一个包含点数为p的连通块. 任何一个连通块都是某棵根属于连通块的子树的上面一部分,所以容易想到用树形DP解决: dp[u][k]表示以u为根的子树中,包含根的大小k的连通块最少的删边数 要求答案就是min(dp[u][p],min(dp[v][p]+1)),u是整棵树的根,v是其他结点 转移从若干个子树各自选择要提供几个k转移,不过指数级时间复杂度,当然又是树上背包了.. 转移好烦,写得我好累好累..还好1A了.. #include<cstdio> #…

题目大意:将一棵n个节点的有根树,删掉一些边变成恰有m个节点的新树.求最少需要去掉几条边. 题目分析:定义状态dp(root,k)表示在以root为根节点的子树中,删掉一些边变成恰有k个节点的新树需要删去的最少边数.对于根节点root的某个儿子son,要么将son及其所有的子节点全部删掉,则dp(root,k)=dp(root,k)+1,只需删除root与son之间的边:要么在son的子树中选出一些边删掉,构造出有j个节点的子树,状态转移方程为dp(root,k)=max(dp(root,k),…

题目大意 给定一棵n个结点的树,问最少需要删除多少条边使得某棵子树的结点个数为p 题解 很经典的树形DP~~~直接上方程吧 dp[u][j]=min(dp[u][j],dp[u][j-k]+dp[v][k]-1) 方程的意思是 以u结点为根保留j个结点需要删除的最少的边的条数,那么可以选择在某个子结点v中选择k个保留,其他结点保留j-k个,为什么需要-1呢,因为相当于把子树v衔接到结点u上,因此边u->v是不需要删除的,所以要-1 代码: #include <iostream> #inc…

[POJ1947]Rebuilding Roads Time Limit: 1000MS   Memory Limit: 30000K Total Submissions: 11934   Accepted: 5519 Description The cows have reconstructed Farmer John's farm, with its N barns (1 <= N <= 150, number 1..N) after the terrible earthquake las…

树形DP..... Rebuilding Roads Time Limit: 1000MS Memory Limit: 30000K Total Submissions: 8188 Accepted: 3659 Description The cows have reconstructed Farmer John's farm, with its N barns (1 <= N <= 150, number 1..N) after the terrible earthquake last Ma…

Rebuilding Roads   Description The cows have reconstructed Farmer John's farm, with its N barns (1 <= N <= 150, number 1..N) after the terrible earthquake last May. The cows didn't have time to rebuild any extra roads, so now there is exactly one wa…

Rebuilding Roads Time Limit: 1000MS Memory Limit: 30000K Total Submissions: 10653 Accepted: 4884 Description The cows have reconstructed Farmer John's farm, with its N barns (1 <= N <= 150, number 1..N) after the terrible earthquake last May. The co…