Possible order of stack output

Tag: The first stack instead of the queue

Assume that the input sequence of the stack is 1234, and determine whether the following 4123,2431 is valid.
For 2431:

First let 1 enter the queue, then let 2 in the queue, let 2 pop up, Let 3 in, let 4 in, and finally pop up in sequence, the result is 2431

For 4123:

To let 4 out of the queue, we must first make 123 all in the queue. Then the order of 4 in the next line should be 3 rather than 1, so it is wrong.

Note:

1. The order of the team members must be kept unchanged.

2. You can also leave the team when you join the team.

3. Because it is a stack, it must be guaranteed to be an advanced post-release. Therefore, we generally first determine the approximate way to join the team based on the first pop-up number in the result to determine whether it is legal.