Rovers

Expert Rovers maps

Expert maps are 8 by 8, with six slots and exactly one program that works, out of thousands. It bends its pattern on the rocks again and again, and there are near misses: programs that pick up every sample but one.

Practice gives you maps you haven't solved yet, as many as you like, and keeps your best time without hints. Every map is made and checked by a computer, so a program that works always fits the slots.

How to play Rovers

1. The rover has to drive over every glowing sample on the map. You don't steer it: you program it.
2. Fill the slots with moves (up, right, down or left), then press Run. The rover makes the moves in order, then starts the program over, again and again, until it has every sample.
3. A move into a rock or off the edge of the map doesn't happen: the rover bumps and stays put, then goes on with the next move. A crater ends the run, and so does going round in circles.

Tap a move to put it in the selected slot; tap a slot to select it, and tap it again to empty it. On a keyboard, the arrow keys write moves, Backspace takes one out and Enter runs the program. A run that fails costs nothing but time: the samples come back, and you can change the program and run it again as often as you like. Your result shows how many runs it took. Empty slots are skipped, so a shorter program works too.

Solving tips

• Look for the pattern. Each time through, the program moves the rover the same way. Find the step the samples repeat, from one to the next, and you've found most of the program.
• Use the walls. A move that bumps is a move that waits. A rover pressed against a wall slides along it, and a rock can turn a pattern exactly where you need it.
• Watch where it went wrong. A failed run leaves its tracks on the map, so you can see the first sample it missed.
• Stuck? A hint puts the right move in one slot of a program that works, keeping as much of yours as it can.