input: Write a function to find the maximum sum of any two distinct elements in the given array. If the array is empty, return 0.
  
  assert find_max_sum([1, 2, 3, 4, 5])==9
  assert find_max_sum([5, 4, 3, 2, 1])==9
  assert find_max_sum([1, 1, 1, 1, 1])==2
  assert find_max_sum([10, 20, 30, 40, 50])==90
  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 and num != max1:
              max2 = num
      return max1 + max2 if max2 != float('-inf') else max1