About Coil

A snake in a walled garden. Eat every apple, then leave through the gate in the hedge, which stays shut until the last apple is gone. The snake moves one square at a time and its body follows exactly where its head has been. It cannot turn back on itself or cross its own body, and every apple makes it one square longer.

That last rule is the whole puzzle. Reaching an apple is easy; leaving again is not, because the snake that arrives is longer than the snake that set out, and it has to turn round in whatever room it left itself. An apple at the end of a narrow alley is a trap unless you eat it early, while the snake is short, or approach it so the body is already pointing the way out. So each garden is a question of order — which apple first, which way round — and of keeping space free near the gate for the long snake at the end.

Every garden was solved by computer before it shipped, so the fewest moves is known exactly and shown as par, and every garden has been checked to need clearly more moves than a snake that never grew would — the body is always part of the problem. The daily challenge gives everyone the same four-apple garden and ranks the day by moves, then time. Undo steps back one move at a time, as far as you like.

Tips to win

• Before moving, find the apple that is hardest to leave — the one in a dead end or a tight corner — and plan to eat it while the snake is still short
• Arrive at a tight apple already facing the way you want to leave, rather than nose first into a corner
• The tail moves out of the way as the head moves: you can follow your own tail round a loop
• Keep the approach to the gate clear; the snake that finishes is the longest one