input: Write a function to improve the time complexity of the given Python program that finds the maximum sum of any two elements in an array. The improved function should use a more efficient algorithm to reduce the nested loop to a single pass through the array.
  
  Function header:
  def find_max_sum(arr):
  
  Assert test cases:
  assert find_max_sum([1, 2, 3, 4, 5]) == 9
  assert find_max_sum([10, 20, 30, 40, 50]) == 90
  assert find_max_sum([5, 15, 10, 20, 30]) == 50
  assert find_max_sum([-1, -2, -3, -4, -5]) == -3
  assert find_max_sum([0, 0, 0, 0, 0]) == 0
  
  Expected Output:
  The function should correctly return the maximum sum of any two elements in the array, utilizing a more efficient approach than the original nested loop method.
output: 
  def find_max_sum(arr):
      if len(arr) < 2:
          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
  