Sudoku vs LITS: Placement Logic and Tetromino Logic Compared

Sudoku decides which symbol belongs in each cell

A standard Sudoku has 81 cells arranged into nine rows, nine columns, and nine 3 by 3 boxes. Each unit must contain all nine symbols exactly once. You solve by eliminating values that conflict with existing placements and by identifying patterns among the remaining candidates. Shapedoku uses this same structure with nine glowing shapes instead of digits. Because each token differs by both shape and color, you can scan visually without treating color as the only identifier. The logical job remains classic Sudoku: every empty cell eventually receives exactly one symbol, and no unit may contain a duplicate. Easy puzzles emphasize direct scanning, while Hard and Extreme grids can require subsets, wings, fish, or chains. The board's regions never change. All uncertainty lives in the values assigned to the cells, which is why pencil Notes are such a natural solving aid.

LITS decides which tetromino belongs in each region

LITS begins with a grid divided into irregular regions. In every region you must shade exactly four orthogonally connected cells so they form one of the tetromino shapes represented by the letters L, I, T, or S. Rotations and reflections count as the same basic shape for the rule about matching neighbors. When two shaded tetrominoes in different regions touch along an edge, they cannot be the same shape. All shaded cells across the entire puzzle must form one connected network, and the shaded cells may not create a solid 2 by 2 block. Instead of assigning one of many values to each cell, you are deciding whether each cell is shaded and which four-cell shape a region ultimately contains. The region borders create local shape candidates, while connectivity and the 2 by 2 restriction create global pressure across those borders.

Think in complete shapes rather than isolated shaded cells

The easiest mistake in LITS is deciding one cell at a time without considering the complete tetromino it must belong to. A stronger approach is to list the possible L, I, T, or S placements within each region. If every legal placement for a region includes one particular cell, that cell must be shaded. If no legal placement uses another cell, it must stay unshaded. This is very similar to candidate intersection in Sudoku: when every surviving possibility shares one fact, that fact is forced. After narrowing a region, inspect neighboring regions for the matching-shape restriction and inspect the whole shaded network for connectivity. Also watch every 2 by 2 area. If three cells are already forced shaded, the fourth must remain unshaded. Sudoku usually moves from local candidate eliminations toward larger patterns. LITS moves between local tetromino possibilities and global network constraints. Choose Sudoku when symbol identity and candidate sets appeal to you. Choose LITS when you prefer spatial shapes, shading, and connectivity. Shapedoku offers a gentle way to explore the Sudoku side, and its first free Hint can help you study a missed deduction instead of turning a difficult solve into guesswork.

1. In Sudoku, identify the possible symbols for each empty cell.
2. In LITS, identify every legal L, I, T, or S placement inside each region.
3. Shade a cell when it appears in every surviving tetromino placement for its region.
4. Leave a cell unshaded when no surviving placement can use it.
5. Check that shaded cells stay connected and never create a solid 2 by 2 block.
6. Use neighboring completed tetrominoes to rule out the same shape touching across a region border.