input: Write a function to find the first non-repeated character in a string.
  assert first_non_repeated_char("aabbcde") == 'c'
  assert first_non_repeated_char("aabbccddeeffg") == 'g'
  assert first_non_repeated_char("xxyz") == 'y'
  assert first_non_repeated_char("abcabc") == None
output: def first_non_repeated_char(s):
      char_count = {}
      for char in s:
          char_count[char] = char_count.get(char, 0) + 1
      for char in s:
          if char_count[char] == 1:
              return char
      return None