input: Write a python function that checks if a string contains an 'a' followed by zero or one 'b'.
  assert check_match("ac")==('Found a match!')
  assert check_match("dc")==('Not matched!')
  assert check_match("abbbba")==('Found a match!')
output: def check_match(text):
      import re
      pattern = 'a[b]?'
      if re.search(pattern, text):
          return 'Found a match!'
      else:
          return 'Not matched!'