Distance Statistics     Description Frustrated at the number of distance queries required to find a reasonable route for his cow marathon, FJ decides to ask queries from which he can learn more information. Specifically, he supplies an integer K (1 <…

  转载请注明出处,谢谢http://blog.csdn.net/ACM_cxlove?viewmode=contents    by---cxlove 上场CF的C题是一个树的分治... 今天刚好又看到一题,就做了下 题意:一棵树,问两个点的距离<=k的点对数目. http://poj.org/problem?id=1987 貌似是经典的点分治题..... 看成有根树,那么这样的点对路径分为两种,1.过根节点,2.存在于某一棵子树当中. 显然情况2可以看成是一种子情况 对于1的统计,统计所有节…

http://poj.org/problem?id=1987 题意:给一棵树,求树上有多少对节点满足距离<=K 思路:点分治,我们考虑把每个距离都存起来,然后排序,一遍扫描计算一下,注意还要减掉自己加自己的方案.而且,我们还要去掉走到同一个子树的方案.复杂度:O(nlog^2n) #include<cstdio> #include<cmath> #include<cstring> #include<iostream> #include<algor…

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…

题目大意:(同poj1741,刷一赠一系列) CODE: #include <cstdio> #include <cstring> #include <iostream> #include <algorithm> #define MAX 40010 #define INF 0x3f3f3f3f using namespace std; int points,edges,k; int head[MAX],total; int next[MAX <<…

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: 16172   Accepted: 5272 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.    …

http://poj.org/problem?id=2255 #include<cstdio> #include <cstring> using namespace std; const int maxn = 27; char pre[maxn],in[maxn]; char past[maxn]; void tre(int ps,int pe,int is,int ie,int& ind) { int lnum = strchr(in,pre[ps]) - in - is…

树的点分治,主要思想是每次找子树的重心,计算经过根节点的情况数,再减去点对属于同一子树的情况. #include <iostream> #include <vector> #include <algorithm> #include <string> #include <string.h> #include <stdio.h> #include <stdlib.h> #include <queue> #inclu…

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…