input: Write a python function to find the first non-repeating character in a string.
  assert first_non_repeating_char("AABCDBAGRQPY") == "C"
  assert first_non_repeating_char("AABBCC") == ""
  assert first_non_repeating_char("XYZXYZABC") == "A"
output: def first_non_repeating_char(s):
      char_count = {}
      for char in s:
          if char in char_count:
              char_count[char] += 1
          else:
              char_count[char] = 1
  
      for char in s:
          if char_count[char] == 1:
              return char
      return ""