input: Write a function to improve the time complexity of finding the maximum sum of any two distinct elements in an array. If the array is empty or contains only one element, return 0 as there are no distinct pairs to sum.
  
  assert find_max_sum([3, 4, 5, 1, 2])==9
  assert find_max_sum([3, 5, 10, 1, 2])==15
  assert find_max_sum([4, 3, 1, 2])==7
  assert find_max_sum([3, 5, 4, 1, 2])==9
  assert find_max_sum([])==0
  assert find_max_sum([7])==0
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 and num != max1:
              max2 = num
      return max1 + max2 if max2 != float('-inf') else 0