input: Write a function to improve the time complexity of the given Python program which calculates the maximum sum of two distinct elements in an array. If the array is empty, return 0.
  def find_max_sum(arr):
      if not arr:
          return 0
      max1, max2 = float('-inf'), float('-inf')
      for num in arr:
          if num > max1:
              max2 = max1
              max1 = num
          elif num > max2:
              max2 = num
      return max1 + max2
  assert find_max_sum([1, 2, 3, 4, 5])==9
  assert find_max_sum([10, 20, 30, 40])==70
  assert find_max_sum([1, 1, 1, 1])==2
  assert find_max_sum([5, 5, 5, 5, 5])==10
  assert find_max_sum([])==0
output: def find_max_sum(arr):
      if not arr:
          return 0
      max1, max2 = float('-inf'), float('-inf')
      for num in arr:
          if num > max1:
              max2 = max1
              max1 = num
          elif num > max2:
              max2 = num
      return max1 + max2