input: Write a function to find the maximum number from a given list of non-negative integers. If the list is empty, return 0.
  assert find_max([3, 1, 7, 4]) == 7
  assert find_max([0, 0, 0, 0]) == 0
  assert find_max([]) == 0
  assert find_max([9, 9, 9, 9]) == 9
  assert find_max([12, 3, 8, 20, 5]) == 20
output: def find_max(nums):
      if not nums:
          return 0
      return max(nums)