Don't pay too much attention to this kind of problem. The probability is too small. It feels more like a brain teaser. The single digit in the question is equal to ten digits, either ten digits or one digit, so the answer is the total number divided by two. It's like 10 people stand in a row and ask how many ways to stand on the right side of Station A and bilibili. If this person doesn't stand on the right side, he stands on the left side of bilibili, and the natural standing method is divided by 2.