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 iand 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]]

For each point, we use a map to track the distance and number of points seen for this distance. Total number of points with same distance should be x * (x - 1) where x is the number of points with a calculated distance from this point.

    public int numberOfBoomerangs(int[][] points) {
        if (points.length == 0) {
            return 0;
        }
        int sum = 0;
        int len = points.length;
        for (int i = 0; i < len; i++) {
            Map distances = new HashMap<>();
            for (int j = 0; j < len; j++) {
                if (i == j) {
                    continue;
                }
                int distance = (points[i][0] - points[j][0]) * (points[i][0] - points[j][0]) + (points[i][1] - points[j][1]) * (points[i][1] - points[j][1]);
                distances.put(distance, distances.getOrDefault(distance, 0) + 1);
            }
            sum += distances.values().stream().mapToInt(x -> x * (x - 1)).sum();
        }
        return sum;
    }