Tower of Hanoi

How to play Tower of Hanoi

1. All the disks start on the left peg, the biggest at the bottom.
2. Tap a peg to pick up its top disk, then tap another peg to drop it. On a keyboard, keys 1, 2 and 3 pick the pegs.
3. Move one disk at a time, and always put a disk on a bigger one or on an empty peg.
4. Rebuild the whole tower on the right peg to win.

Tips

• With an odd number of disks, move the smallest disk first to the right peg; with an even number, to the middle peg.
• The smallest disk moves every other turn, always in the same direction around the pegs.
• Between two moves of the smallest disk, there is only one legal move left: make it.
• The best possible score is 2 to the power of the number of disks, minus 1: 7 moves for 3 disks, 31 for 5.
• Stuck after a few wrong moves? Hint shows the best next move from where you are, and Undo takes a move back. The diamond badge is for a perfect tower with neither.

About Tower of Hanoi

The Tower of Hanoi was invented by the French mathematician Edouard Lucas in 1883. A legend tells of monks moving 64 golden disks: at one move per second, they would need almost 600 billion years.

It is a perfect lesson in breaking a big problem into smaller ones: to move a tower of five disks, first move the four on top, then the big one, then the four again. Four levels go from 3 to 6 disks, and the game tells you when you hit the perfect score.

Points and badges

Finishing a game of Tower of Hanoi earns points for your level. Four badges are waiting in this game, from bronze to diamond: each one says what to do and adds bonus points.

Questions