Tree   Description Give a tree with n vertices,each edge has a length(positive integer less than 1001). Define dist(u,v)=The min distance between node u and v. Give an integer k,for every pair (u,v) of vertices is called valid if and only if dist(u,v…

Tree Time Limit: 1000MS   Memory Limit: 30000K Total Submissions: 18205   Accepted: 5951 Description Give a tree with n vertices,each edge has a length(positive integer less than 1001). Define dist(u,v)=The min distance between node u and v. Give an…

                                                                                             POJ 1741 Tree Description Give a tree with n vertices,each edge has a length(positive integer less than 1001). Define dist(u,v)=The min distance between node…

poj 1741 Tree(树的点分治) 给出一个n个结点的树和一个整数k,问有多少个距离不超过k的点对. 首先对于一个树中的点对,要么经过根结点,要么不经过.所以我们可以把经过根节点的符合点对统计出来.接着对于每一个子树再次运算.如果不用点分治的技巧,时间复杂度可能退化成\(O(n^2)\)(链).如果对于子树重新选根,找到树的重心,就一定可以保证时间复杂度在\(O(nlogn)\)内. 具体技巧是:首先选出树的重心,将重心视为根.接着计算出每个结点的深度,以此统计答案.由于子树中可能出现重复…

http://poj.org/problem? id=1741 Description Give a tree with n vertices,each edge has a length(positive integer less than 1001).  Define dist(u,v)=The min distance between node u and v.  Give an integer k,for every pair (u,v) of vertices is called va…

poj 1655:http://poj.org/problem?id=1655 题意: 给无根树,  找出以一节点为根,  使节点最多的树,节点最少. 题解:一道树形dp,先dfs 标记 所有节点的子树的节点数. 再dfs  找出以某节点为根的最大子树,节点最少. 复杂度(n) /***Good Luck***/ #define _CRT_SECURE_NO_WARNINGS #include <iostream> #include <cstdio> #include <cs…

POJ 1741. Tree Time Limit: 1000MS   Memory Limit: 30000K Total Submissions: 34141   Accepted: 11420 Description Give a tree with n vertices,each edge has a length(positive integer less than 1001). Define dist(u,v)=The min distance between node u and…

写的第一道点分治的题目,权当认识点分治了. 点分治,就是对每条过某个点的路径进行考虑,若路径不经过此点,则可以对其子树进行考虑. 具体可以看menci的blog:点分治 来看一道例题:POJ 1741 Tree 题目大意:扔给你一颗有权无根树,求有多少条路径的长度小于k: 解题思路:先找出重心,用一次dfs处理出每个点到根的距离dis,然后将dis[]排序,用O(n)的复杂度处理出"过根且长度小于等于k的路径数目",删除根节点,对于每棵子树重复上述操作. 注意要去重: 像上面这样一个图…

Tree Time Limit: 1000MS   Memory Limit: 30000K Total Submissions: 21357   Accepted: 7006 Description Give a tree with n vertices,each edge has a length(positive integer less than 1001).Define dist(u,v)=The min distance between node u and v.Give an in…

题链: http://poj.org/problem?id=1741题解: 树上点分治. 入门题,不多说了. 代码: #include<cstdio> #include<cstring> #include<iostream> #include<algorithm> #include<queue> #define MAXN 10004 using namespace std; struct EDGE{ int ent; int to[MAXN*2]…