A8492. Number of Triplets
编程题
普及/提高-
知识点
题目描述
You are given $n$ points on a plane. All points are different.
Find the number of different groups of three points $(A,B,C)$ such that point $B$ is the middle of segment $AC$ .
The groups of three points are considered unordered, that is, if point $B$ is the middle of segment $AC$ , then groups $(A,B,C)$ and $(C,B,A)$ are considered the same.
Find the number of different groups of three points $(A,B,C)$ such that point $B$ is the middle of segment $AC$ .
The groups of three points are considered unordered, that is, if point $B$ is the middle of segment $AC$ , then groups $(A,B,C)$ and $(C,B,A)$ are considered the same.
输入格式
The first line contains a single integer $n$ ( $3<=n<=3000$ ) — the number of points.
Next $n$ lines contain the points. The $i$ -th line contains coordinates of the $i$ -th point: two space-separated integers $x_{i},y_{i}$ ( $-1000<=x_{i},y_{i}<=1000$ ).
It is guaranteed that all given points are different.
Next $n$ lines contain the points. The $i$ -th line contains coordinates of the $i$ -th point: two space-separated integers $x_{i},y_{i}$ ( $-1000<=x_{i},y_{i}<=1000$ ).
It is guaranteed that all given points are different.
输出格式
Print the single number — the answer to the problem.
输入输出样例
输入 #1
3 1 1 2 2 3 3
输出 #1
1
输入 #2
3 0 0 -1 0 0 1
输出 #2
0