arr.sort!
  min_diff = 10000000
  result = {}
  
  (0..(arr.size - 2)).each do |i|
    diff = (arr[i+1] - arr[i]).abs
    if diff <= min_diff
      min_diff = diff
      result[diff] ||= []
      result[diff] << [arr[i], arr[i+1]]
    end
  end
  result[min_diff]