FindMissing.py

def _ConsumeString(str_value, last, has_jumped):
 """Consumes the string value.

 Args:
 last: The last number that was read.
 has_jumped: Whether we have skipped a number.

 Returns:
 A tuple of a success boolean (for whether we have read the whole string),
 and the missing number.
 """
 next1 = str(last + 1)
 if str_value.startswith(next1):
 return _ConsumeString(str_value[len(next1):], last + 1, has_jumped)
 elif not has_jumped:
 next2 = str(last + 2)
 if str_value.startswith(next2):
 success, _ = _ConsumeString(str_value[len(next2):], last + 2, True)
 return success, last + 1 if success else None
 else:
 return False, None
 else:
 return not str_value, None


def FindMissing(str_value):
 """Finds the missing consecutive number in the string value."""
 for i in range(1, len(str_value) / 2):
 try:
 first = int(str_value[0:i])
 success, jumped = _ConsumeString(str_value[i:], first, False)
 if success:
 return jumped
 except ValueError:
 continue
 return -1


print FindMissing("12345689101112")
print FindMissing("9991000100110021004")
# There's no missing number, so it should return -1.
print FindMissing("123456789101112")