447. Number of Boomerangs

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] (inclusive).

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]]

class Solution {
    public int numberOfBoomerangs(int[][] points) {
        int res = 0;
        for(int i = 0; i < points.length; i++){
            Map<Integer, Integer> map = new HashMap();
           for(int j = 0; j < points.length; j++){
                if(i == j) continue;
                
                int k = help(points[i], points[j]);
                map.put(k, (map.getOrDefault(k, 0)) + 1);
            }
            for(int t: map.values()) res += t*(t-1);
        }
         return res;   
    }
    public int help(int[] a, int[] b){
        int t1 = a[0] - b[0];
        int t2 = a[1] - b[1];
        return t1*t1 + t2*t2;
    }
}

https://www.cnblogs.com/grandyang/p/6049382.html