1. The Hanoi Tower, also known as the River Tower Problem, originated from an ancient Indian puzzle toy. When creating the world, three diamond pillars were made, and 64 golden disks were stacked in size order from bottom to top on one pillar. The disks were then rearranged in size order from bottom to top on another pillar, and it was stipulated that the disks could not be enlarged on the small disk, and only one disk could be moved between the three pillars at a time.
2. The first step for ABC three needles is to move the first n-1 from A to B, the last time is to move n to C, the second step is to move n-1 from B to C, and the last time is to move 1 to C, which is the termination condition. It will not stop until n=1, and then continue to return to this line and run the following code every time. Note that here the parameter xyz starts calling itself, so the parameter order changes.