
ZOJ Problem Set  2496
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 4element subsets of these points that can be written as {A, B, C, D} such that AB  CD, and BC  AD. No four points are in a straight line. Input Specification The first line of the input file contains a single integer t (1 <= t <= 10), the number of test cases. It is followed by the input data for each test case. The first line of each test case contains an integer n (1 <= n <= 1000). Each of the next n lines, contains 2 spaceseparated integers x and y (the coordinates of a point) with magnitude (absolute value) of no more than 1000000000. Output Specification Output should contain t lines. Line i contains an integer showing the number of the parallelograms as described above for test case i. Sample Input 2 6 0 0 2 0 4 0 1 1 3 1 5 1 7 2 1 8 9 5 7 1 1 4 8 2 0 9 8 Sample Output 5 6 Source: Asia 2004, Tehran (Iran), Sharif Preliminary 