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What Is LITS?

LITS (also known as Nuruomino) is a region-based tetromino logic puzzle first created by the Japanese puzzle designer Naoki Inaba and later popularised by Nikoli. The name “LITS” comes from the four tetromino shapes used in the puzzle: L, I (straight), T, and S (skew). In the Nikoli catalogue it also goes by the name “Nuruomino” (“nuru” meaning “to paint”).

The puzzle is played on a rectangular grid that has been pre-divided into irregular regions (sometimes called “rooms” or “cages”). Your task is to shade exactly four cells in each region so that those four cells form one of the four LITS tetrominoes. The result is a grid where every region contains exactly one tetromino and all the shaded cells obey a set of global constraints.

Rules of LITS

1. One tetromino per region: In every region you must shade exactly four cells that form one of the four tetrominoes — L (including its mirror J), I, T, or S (including its mirror Z). Rotations and reflections of the same shape count as the same type.
2. Connected shading: All shaded cells on the entire grid must form a single orthogonally connected group. You should be able to travel from any shaded cell to any other shaded cell moving only up, down, left, or right through shaded cells.
3. No 2×2 pools: No 2×2 block of cells may all be shaded. This constraint prevents large featureless dark areas and provides key deduction points.
4. No same-type adjacency: Two tetrominoes of the same type may not share an orthogonal edge. For example, an L-tetromino’s cells cannot be directly adjacent (horizontally or vertically) to the cells of another L-tetromino. Different types can be adjacent.

How to Solve LITS — Strategy Tips

1. Start With Small Regions

Regions with exactly four cells have only one possible tetromino placement — all four cells must be shaded. Identify these first. Regions with five cells have very few possible placements, so they are the next easiest to resolve.

2. Apply the No-2×2-Pool Rule

After shading some cells, check every potential 2×2 block. If three of the four cells in a block are already shaded, the fourth cannot be shaded. This frequently eliminates tetromino placements that would create a pool. This rule drives many of the key deductions in a LITS puzzle.

3. Check Connectivity Early

All shaded cells must form one connected group. If a candidate tetromino placement would strand a pocket of shaded cells (making them disconnected from the rest), that placement is impossible. Think about how new tetrominoes will connect to the growing shaded area.

4. Use the Same-Type Adjacency Rule

Once you know the type of a tetromino in one region, its neighbouring regions are constrained. If a region’s tetromino is an L, then every adjacent region must use I, T, or S — never another L. This “graph colouring” style constraint can drastically reduce options.

5. Enumerate Possible Shapes

For each region, list the possible tetromino placements (shape + position) that fit inside the region. Cross off any that violate the pool, connectivity, or same-type rules. Often a region will have only one or two valid placements, making the deduction straightforward.

6. Work From the Edges

Regions along the grid border are more constrained because their tetrominoes cannot extend beyond the edge. This limits the possible shapes and positions, giving you a good starting point.

Grid Sizes & Difficulty Levels

• 7×7 — Easy: A compact grid with fewer regions. Ideal for learning the rules. Most puzzles solve in two to five minutes.
• 7×7 — Medium/Hard: Same grid size but more regions (more tetrominoes), creating tighter interactions between constraints.
• 10×10: A well-balanced LITS experience. Enough space for complex interactions without being overwhelming.
• 12×12: Large grids for experienced solvers. Many regions, intricate connectivity paths, and demanding constraint chains.

LITS vs Other Logic Puzzles

• vs Nurikabe: Both involve shading cells on a grid with connectivity and no-2×2-pool rules. Nurikabe uses numbered island clues while LITS uses tetromino shape constraints and region partitions.
• vs Shikaku: Both partition a grid into regions, but Shikaku divides the grid into rectangles of specified areas. LITS shades tetrominoes within pre-given regions.
• vs Sudoku: Sudoku fills numbers into a Latin-square grid. LITS shades shapes into regions with spatial constraints — a very different style of logic.
• vs Tapa: Tapa also shades cells to form a connected wall with no 2×2 pools. Its clue mechanism (numbers indicating consecutive group lengths) differs from LITS’s tetromino-in-region approach.
• vs Pentominoes: Pentomino puzzles use five-cell pieces. LITS uses four-cell tetrominoes and adds the connectivity and same-type-adjacency constraints that Pentomino tiling problems lack.

The Four Tetrominoes

Every region must contain exactly one of these shapes. Rotations and reflections are allowed — an L and its mirror (J) are considered the same type, as are S and its mirror (Z).

• L-tetromino: An “L” or “J” shape — three cells in a line with one cell extending perpendicularly from one end.
• I-tetromino: Four cells in a straight line, either horizontal or vertical.
• T-tetromino: Three cells in a line with one cell extending perpendicularly from the centre — like the letter T.
• S-tetromino: An “S” or “Z” shape — two cells in one row and two in the adjacent row, offset by one column.

Frequently Asked Questions

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