LeetCode [447] Number of Boomerangs

447. Number of Boomerangs

Easy

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 n = points.length;
        int ret = 0;
        for(int i=0; i<n; ++i){
            Map<Integer, Integer> map = new HashMap<>();
            for(int j=0; j<n; ++j){
                if(i==j) continue; 
                int d = (int)Math.pow(points[i][0]-points[j][0], 2) + (int)Math.pow(points[i][1]-points[j][1], 2);
                map.put(d, map.getOrDefault(d, 0)+1);
            }
            
            for(Map.Entry<Integer,Integer> e : map.entrySet()){
                int c = e.getValue();
                ret += c*(c-1);
            }
        }
        return ret;
    }
}