input: Write a function to find the minimum absolute difference in an array.
  assert minimumAbsDifference([2, 9, 6, 5, 4, 9, 8]) == 1
  assert minimumAbsDifference([1, 3, 6, 10, 15]) == 2
  assert minimumAbsDifference([4, 4, 4, 4]) == 0
output: def minimumAbsDifference(arr):
      arr.sort()
      min_diff = float('inf')
      for i in range(1, arr.length):
          min_diff = min(min_diff, abs(arr[i] - arr[i-1]))
      return min_diff