Sleepy Faces Strategy: Chase the Lights Method

By Nesim Razon, independent Android developer

Sleepy Faces is a light-toggling puzzle: tapping a face flips it and its four neighbors, and you must wake every sleepy face. It looks random, but a simple method always works.

The rules

Each face is awake (yellow) or asleep (blue). Tapping a face flips that face and the faces directly above, below, left and right of it. Wake every face to win.

• Tapping the same face twice cancels out, so every face needs at most one tap.
• The order of your taps does not matter, only which faces you tap.
• Every board in Logiclings can be solved.

Chase the lights, row by row

Work from the top row down. Whenever a face in a row is still asleep, tap the face directly below it. That wakes it without touching any row above.

• Start at the top left and go left to right, then move to the next row.
• After you finish the second-to-last row, every row except the bottom one is awake.
• If the bottom row is fully awake too, you are done.

If the bottom row still has sleepy faces (5x5 cheat sheet)

The leftover pattern in the bottom row tells you which top-row faces to tap first. Undo back to the start (or press Reset), tap those top-row faces, then chase the lights again. Write sleepy as 1 and awake as 0, columns from left to right:

• 00111: tap column 4 first
• 01010: tap columns 1 and 4 first
• 01101: tap column 1 first
• 10001: tap columns 1 and 2 first
• 10110: tap column 5 first
• 11011: tap column 3 first
• 11100: tap column 2 first

Other board sizes

On 6x6 and 7x7 boards every starting position has exactly one solution, so there is only one set of faces to tap. On 4x4 and 5x5 boards there can be several solutions, and Logiclings counts the one with the fewest taps as the best.

Hints that teach

In Logiclings a hint uses the chase method: it taps the face below the first sleepy face and tells you why, so every hint is also a small lesson.