Push each barrel (purple square) into a target (yellow ring). Barrels can be pushed up, down, left or right, but not into another barrel or the wall.
On a touch screen, a tap does what a click does.
Tap or click any square you can reach to walk there, the shortest way round. Walking never pushes a barrel.
To push, drag a barrel the way you want it to go, and you walk round behind it first; or press on your character and drag toward a barrel beside you. An arrow, and a ghost barrel on the square it ends on, show where the barrel will stop: one square further for each square you drag, as far as it can go before a wall or another barrel. A barrel you can’t get behind shows no arrow. Let go to push. Drag back to where you started before letting go to change your mind.
With a keyboard, use the arrow keys or the numeric keypad. Each press takes one step, and walking into a barrel pushes it. The digit keys work like the numeric keypad even without one: 8 is up, 2 down, 4 left and 6 right, and 7, 9, 1 and 3 step diagonally. A diagonal step only walks, and only past a corner with room to go round it.
Hint shows the next push rather than making it. No push in Sokoban is forced by logic, so the hint searches for a line of pushes that gets every barrel onto a target and shows you one push from it: the barrel rings, and so does the square it goes into. Played by the hint, the push walks you round to the barrel first.
You can never pull a barrel, so the pushes to watch for are the ones you can’t take back. A barrel pushed into a corner can never come out. A barrel pushed against a wall can only slide along it, and if no target lies that way it can never reach one. Two barrels side by side against a wall, or four in a square, can never move again. Any of these off a target means the puzzle can no longer be finished.
So the first thing the hint looks for is another way to push the same barrel that would leave it, or a barrel beside it, stuck like that. It stripes that push and shows one that keeps the barrel free.
Otherwise, when the search has checked the barrel’s other pushes, the hint says what it found: it draws an arrow on each way the barrel can still be pushed and finish, the suggested one among them, and says when no other way can.
Most of the skill in Sokoban is the order the barrels go home in, so that is what the hint says next, where it applies:
When none of that applies, it says what the push does that you can see: that it puts the barrel on a target, or that it lets you out when barrels have shut you into a small part of the board.
The hint refuses when there is nothing to search for: if a barrel off its target is already stuck, it outlines that barrel and asks you to undo, and it asks the same when the search proves no line of pushes from here can finish. A position can also be too tangled for the search to settle, and the hint says so; Show solution… then shows the finished board, from the board as it was dealt if not from yours. Boards are dealt so that the hint can see them through from the start; only a custom board much larger than the ones on the Type menu may be past it.
Check & save asks the same question, since Sokoban has no single answer to check your pushes against: it won’t save a position the hint would ask you to undo from, and outlines the stuck barrel.
These parameters are available from the ‘Custom type…’ option on the ‘Type’ menu.