B won. B crossed out 7 and 9 twice before. Conclusion: The first row will win.
Two cardinal numbers: A: If there are 3, 4 and 5 left, the first player wins; B: If there are 8 left, the first player loses.
Draw 678, and there are five left at both ends. One is 12. Anyway, five can only be drawn once.
(1) If the opponent draws first 12:
12 No matter how his opponent ranks first, his backhand can make his opponent rank last 12 (both himself and his opponent want each other to rank last).
Method: If the opponent has 0 left at one end and 9 left at the other end, draw 3 of 9 (2 left at one end, 4 left at one end or 1 left at one end, 5 left at one end, and the opponent can only draw 4 or 5).
Similarly, opponents keep 1 or 2 heads, 7 or 8 heads, no more than 5 heads in this platoon (within 7 or 8 heads), and no more than 2 heads in the rest.
If the opponent leaves three at one end and six at the other end, he chooses the middle of the six and can't row in the six. The other side can only rank third at the other end.
If the opponent leaves four at one end and five at the other end, the opponent's row 12 is the last row.
(2) If the opponent draws five cards first:
In 12, no matter how your opponent draws, you can let yourself draw the last stroke in 12 first (both yourself and your opponent want to draw the last stroke). Method: Party B can draw three, leave eight at one end and 1 at the other end. Let the opponent rank eight first. No matter how you row, your opponent will lose (according to B).