NumberOfBoomerangs.java

import java.util.HashMap;

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// 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 result = 0;

        for (int[] basePoint : points) {
          HashMap<Integer, Integer> distanceToCount = new HashMap<>();

          for (int[] point : points) {
            int deltaX = basePoint[0] - point[0];
            int deltaY = basePoint[1] - point[1];
            int distance = deltaX * deltaX + deltaY * deltaY;
            distanceToCount.put(distance, distanceToCount.getOrDefault(distance, 0) + 1);
          }

          for (Integer count : distanceToCount.values()) {
            result += count * (count - 1);
          }
        }

        return result;
    }
}