input: Write a python function to calculate the probability of any two values in the array being equal.
  assert get_probability_of_equal([1, 2, 3, 3, 4, 5]) == 0.03333333333333333
  assert get_probability_of_equal([1, 1, 1, 1]) == 1.0
  assert get_probability_of_equal([1, 2, 3, 4, 5, 6]) == 0.0
output: def get_probability_of_equal(arr):
      from collections import Counter
      n = len(arr)
      if n < 2:
          return 0.0
      
      counter = Counter(arr)
      total_pairs = n * (n - 1) / 2
      equal_pairs = sum(count * (count - 1) / 2 for count in counter.values())
      
      return equal_pairs / total_pairs if total_pairs else 0.0