About Knight Swap
Knight swapping puzzles are among the oldest chess puzzles of all: in 1512 Paolo Guarini set two white and two black knights in the corners of a 3 × 3 board and asked how to swap them. Knights move as they do in chess, in an L of two squares and one, and here they never take each other, so they have to file around the board to get past. This page has seven of these puzzles, from one knight of each colour to a 3 × 5 board with eight knights and only seven empty squares. Every one has been solved by a program, so the page knows the fewest moves.
How to play Knight Swap
- Tap a knight, then a lit square to move it there. Knights move as in chess, two squares one way and one square the other, and only onto empty squares.
- You can also tap an empty square that only one knight can reach.
- Put every white knight where a black one started and every black knight where a white one started. A small dot on each square shows which colour ends there.
- The fewest possible moves earn three stars. Your progress is saved on this device only.
Tips & strategy
- Picture the knight moves as a loop: on a 3 × 3 board the eight outer squares form one ring of knight moves, and the centre can’t be reached at all.
- On a ring nobody can overtake, so every knight has to travel the same way round.
- Move the knights in turn rather than sending one far ahead: a knight that runs ahead often sits on the square another one needs.
- The dots on the squares show where each colour has to end, so count how far each knight still has to go.
Knight Swap: questions and answers
How many moves does Guarini’s puzzle take?
Sixteen. The eight outer squares of the 3 × 3 board form one loop of knight moves, and each of the four knights has to go four steps round it.
Can knights take each other?
No. In this puzzle a knight only moves onto an empty square, so the knights have to make room for each other.
Is my progress saved?
Yes, in your browser on this device: the puzzles you have solved, your stars and your best result for each.