題目：

Given n points in the plane that are all pairwise distinct, a "boomerang" is a tuple of points (i, j, k) such that the distance between i and j equals the distance between i and k (the order of the tuple matters).

Find the number of boomerangs. You may assume that n will be at most 500 and coordinates of points are all in the range [-10000, 10000]

Example:

Input:
[[0,0],[1,0],[2,0]]

Output:
2

Explanation:
The two boomerangs are [[1,0],[0,0],[2,0]] and [[1,0],[2,0],[0,0]]

程式碼：

class Solution {
    public int numberOfBoomerangs(int[][] points) {
        int all = 0;
        int n = points.length;
        for(int i = 0; i < n; i++){
            Map<Integer, Integer> m = new HashMap<>();
            for(int j = 0; j < n; j++){
                Integer dis = (points[i][0]-points[j][0])*(points[i][0]-points[j][0])+ (points[i][1] - points[j][1]) * (points[i][1] - points[j][1]);
                m.put(dis, m.getOrDefault(dis, 0)+1);
            }
            for(int num : m.values()){
                if(num > 1) all += num *(num - 1);
            }
            
        }
        return all;
    }
}