input: Write a function to find the first non-repeating character in a given list. If there is no non-repeating character, return None.
  
  def first_non_repeating_char(lst):
      dct = {}
      
      for l in lst:
          if l in dct:
              dct[l] += 1
          else:
              dct[l] = 1
              
      for l in lst:
          if dct[l] == 1:
              return l
              
      return None
  
  assert first_non_repeating_char([1, 2, 3, 4, 4, 3, 2, 1]) == None
  assert first_non_repeating_char([1, 2, 3, 4, 5, 6]) == 1
  assert first_non_repeating_char([7, 7, 8, 9, 9, 10]) == 8
  assert first_non_repeating_char([]) == None
output: def first_non_repeating_char(lst):
      dct = {}
      
      for l in lst:
          if l in dct:
              dct[l] += 1
          else:
              dct[l] = 1
              
      for l in lst:
          if dct[l] == 1:
              return l
              
      return None