This is game to play by yourself. You will need a game board and 8 counters (or buttons or coins) - 4 of one colour and 4 of another colour.
Place 4 counters in the top row and 4 in the bottom row. The aim is for the top counters to swap places with the bottom counters using the smallest possible number of moves. You can slide a counter one square at a time, with no jumping or sharing a square.
Record your moves so that you can count them and find the best way to solve the puzzle.
It might help to number the squares.
Click here to try an interactive version.