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]]

Solution

public class Solution {
    public int numberOfBoomerangs(int[][] points) {
        if(points.length == 0) return 0;
        int cnt = 0;
        for(int i = 0; i < points.length; i++) {
            Map<Integer, Integer> map = new HashMap<Integer, Integer>();
            for(int j = 0; j < points.length; j++) {
                if(i == j) continue;
                int dist = (points[i][0] - points[j][0]) * (points[i][0] - points[j][0]) + 
                            (points[i][1] - points[j][1]) * (points[i][1] - points[j][1]);
                if(!map.containsKey(dist)) map.put(dist, 0);
                map.put(dist, map.get(dist)+1);
            }
            for(Integer key: map.keySet()) {
                int val = map.get(key);
                if(val > 1) cnt += val * (val - 1);
            }
        }
        return cnt;
    }
}