A boomerang is an ordered triple of points (i, j, k) where the distance from i to j equals the distance from i to k, and j and k are different points. The order matters, so (i, j, k) and (i, k, j) count separately.
Given an array points of distinct [x, y] pairs, return the number of boomerangs.
[[0,0],[1,0],[2,0]] returns 2: the middle point is the centre of (1,0), (0,0), (2,0) in either order- Use the squared distance as the key; it is an exact integer, unlike the square root
- Target: O(n2) time. The tests use n = 800