How to play LITS
- Look at the regions. The grid is divided into regions by thick lines. Each region will hold exactly one tetromino: four shaded squares joined side by side.
- Shade four squares per region. Tap a square to shade it. Switch to Mark empty to put a dot on squares you know stay blank. Drag to shade or dot several squares in one stroke.
- Keep all shading connected. When you are done, every shaded square must be reachable from every other one by stepping side by side through shaded squares, across region borders.
- No 2×2 shaded block. Four shaded squares may never form a 2×2 square anywhere on the board, even if they come from different regions.
- Matching shapes may not touch. There are four tetromino shapes: L, I, T and S (mirror images and rotations count as the same shape). Two tetrominoes of the same shape in neighbouring regions may not share an edge.
The four LITS shapes
These are four of the five tetrominoes. The fifth, the 2×2 square, is ruled out by the no-2×2 rule. Rotating or flipping a piece does not change its shape, so an L never touches a J and an S never touches a Z in a neighbouring region.
LITS rules with an example
- One tetromino per region. The big outer region gets an I down the left side, the small top region a T, the middle region an L and the right region an I.
- All shading connects. The second and fourth rows link every piece into one group.
- No 2×2. Look around the T: the gaps in the middle row keep every 2×2 window at three shaded squares or fewer.
- Equal shapes apart. The two I pieces sit on opposite edges and never share a side.
LITS strategy: where to start
- Four-square regions are free. A region of exactly four squares must be shaded completely. Shade it first, then dot around it where its shape forbids a twin.
- Find the squares every placement uses. In a narrow region, list the tetrominoes that fit. A square that is shaded in all of them can be shaded now; a square used by none can be dotted.
- Break 2×2 windows early. When three squares of a 2×2 are shaded, the fourth gets a dot. This often decides which way a piece bends.
- Think about connection. A region far from the rest must still link up, so its tetromino has to reach toward a neighbour. Cut-off pockets of dots are a warning sign.
- Use the shape rule both ways. If a neighbouring region already holds a T, a T in this region cannot touch it — which can rule out half the options in one go.
Not sure? Check shows which squares cannot be right, and Hint fixes a mistake or shades one correct square in the region you have worked on most.
The 20 levels
All levels are original. For each one we first laid out a valid set of tetrominoes, grew a region around each, then reshaped region borders until our solver proved there was exactly one solution.
LITS and other tetromino puzzles
In the tetromino puzzle you pack given pieces into a frame; in LITS you have to find where the pieces are hidden. If you like that kind of deduction, Fillomino uses numbers to describe hidden polyominoes of every size. Bigger pieces wait in the polyomino and hexomino puzzles, and the pentomino shapes guide explains how polyominoes are counted.