Disc Tower
Move a stack of discs from the left peg to the right peg, one disc at a time, never putting a bigger disc on a smaller one. Can you match the fewest possible moves?
How to play
- All the discs start stacked on the left peg, biggest at the bottom. Move the whole stack to the right peg.
- Tap a peg to pick up its top disc, then tap the peg where it should go. Keys 1, 2 and 3 pick the left, middle and right pegs.
- You can only move one disc at a time, and a disc can never sit on a smaller one.
- Choose from 3 to 8 discs. A stack of n discs can be solved in 2 to the power n, minus 1 moves, and that is the number to beat. Hint shows a good next move from anywhere.
Tips and strategy
- To move a stack of n discs, move the top n minus 1 to the spare peg, move the big disc across, then bring the n minus 1 on top of it.
- With an odd number of discs, the smallest disc moves toward the right peg each time it moves. With an even number, it goes toward the middle one.
- Move the smallest disc every other turn. The in-between moves are forced, because only one other move is legal.
- Solve three discs perfectly in 7 moves first, then go up. Each extra disc roughly doubles the moves.
FAQ
- Why is the fewest-moves number so big for 8 discs?
- Each extra disc doubles the work and adds one. Eight discs need 255 moves, and no cleverness can do it in fewer.
- What does the Hint button do?
- It highlights the two pegs of a move that is part of a shortest solution from your current position. It does not make the move for you.
- Is my best saved?
- Yes. Your fewest moves for each stack size is saved in your browser.