Parallelogram Counting Time Limit: 5000MS   Memory Limit: 65536K Total Submissions: 6895   Accepted: 2423 Description There are n distinct points in the plane, given by their integer coordinates. Find the number of parallelograms whose vertices…

题目链接: http://poj.org/problem?id=1971 题意: 二维空间给n个任意三点不共线的坐标,问这些点能够组成多少个不同的平行四边形. 题解: 使用的平行四边形的判断条件:对角线互相平分的四边形是平行四边形. 所以我们枚举每一条线段,如果有两条线段的中点是重合的,那么这四个顶点就能构成一个平行四边形,也就是说每条线段我们只要维护中点就可以了. 1.map维护中点:(数据比较大,t了) #include<iostream> #include<cstdio> #…

Description There are n distinct points in the plane, given by their integer coordinates. Find the number of parallelograms whose vertices lie on these points. In other words, find the number of 4-element subsets of these points that can be written a…

Parallelogram Counting Time Limit: 5000MS   Memory Limit: 65536K Total Submissions: 5749   Accepted: 1934 Description There are n distinct points in the plane, given by their integer coordinates. Find the number of parallelograms whose vertices lie o…

1058 - Parallelogram Counting    PDF (English) Statistics Forum Time Limit: 2 second(s) Memory Limit: 32 MB There are n distinct points in the plane, given by their integer coordinates. Find the number of parallelograms whose vertices lie on these po…

1058 - Parallelogram Counting There are n distinct points in the plane, given by their integer coordinates. Find the number of parallelograms whose vertices lie on these points. In other words, find the number of 4-element subsets of these points tha…

题目链接:http://poj.org/problem?id=1971 题意:给定n个坐标.问有多少种方法可以组成平行四边形.题目保证不会有4个点共线的情况. 思路:可以发现平行四边形的一个特点,就是对角线相交后得到的点.如果两点线的中点相交,那么这两条线就可以组成一个平行四边形[不需去排除4点共线],所以枚举两两组合的点对HASH成中点.然后判断所有中点,如果某个中点出现了K次,那么可以组成K*(K-1)/2个平行四边形. 用map来判断某个中点出现次数会TLE,所以可以对中点进行排序后判重复…

Lake Counting Time Limit: 1000MS     Memory Limit: 65536K Total Submissions: 17917     Accepted: 9069 Description Due to recent rains, water has pooled in various places in Farmer John's field, which is represented by a rectangle of N x M (1 <= N <=…

http://poj.org/problem?id=2386 http://acm.hdu.edu.cn/showproblem.php?pid=1241 求有多少个连通子图.复杂度都是O(n*m). #include <cstdio> ][]; int n,m; void dfs(int x,int y) { ;i<=;i++) ;j<=;j++) //循环遍历8个方向 { int xx=x+i,yy=y+j; &&xx<n&&yy>=…

Lake Counting Time Limit: 1000MS   Memory Limit: 65536K Total Submissions: 28966   Accepted: 14505 Description Due to recent rains, water has pooled in various places in Farmer John's field, which is represented by a rectangle of N x M (1 <= N <= 10…