input: Write a function to find the maximum element in the given array.
  assert find_max_element([1, 10, 50, 3, 8])==50
  assert find_max_element([-1, -10, -50, -3, -8])==-1
  assert find_max_element([1])==1
  assert find_max_element([5, 5, 5, 5])==5
  assert find_max_element([])==None
output: def find_max_element(arr):
      if not arr:
          return None
      max_element = arr[0]
      for num in arr:
          if num > max_element:
              max_element = num
      return max_element