447. Number of Boomerangs

You are given n points in the plane that are all distinct , where points[i] = [xi, yi]. 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).

Return the number of boomerangs.

Example 1:

Input: points = [[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]].

Example 2:

Input: points = [[1,1],[2,2],[3,3]]
Output: 2

Example 3:

Input: points = [[1,1]]
Output: 0

Constraints:

• n == points.length
• 1 <= n <= 500
• points[i].length == 2
• -104 <= xi, yi <= 104
• All the points are unique.

# @lc code=start
using LeetCode

function number_of_boomerangs(points::Vector{Vector{Int}})::Int
    res = 0
    for p in points
        distance_frequency = DefaultDict(0)
        for q in points
            p == q && continue
            dis = (p[1] - q[1])^2 + (p[2] - q[2])^2
            distance_frequency[dis] += 1
        end

        for k in values(distance_frequency)
            k > 1 && (res += k * (k - 1))
        end
    end

    return res
end
# @lc code=end

number_of_boomerangs (generic function with 1 method)

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