K-diff Pairs in an Array

find_pairs.rb

# @param {Integer[]} nums
# @param {Integer} k
# @return {Integer}
def find_pairs(nums, k)
    if k == 0
        return nums.group_by { |n| n }
            .map { |k, v| [k, v.size] }
            .filter { |(n, c)| c >= 2 }
            .size
    end
    
    a = Set.new nums
    a.inject(0) { |m, n| a.include?(n + k) ? m + 1 : m }
end