Shakashaka is a celebrated Nikoli logic puzzle that blends spatial geometry with strict deduction. The grid contains empty white cells and pre-printed black wall blocks, some containing numbers from 0 to 4.

• Triangle Placement: Each white cell can either stay completely empty (white) or hold one of four black right-angled triangles (◤, ◥, ◣, ◢), covering exactly half the cell.
• Orthogonal Clues: A number in a black cell specifies how many triangles must touch its 4 orthogonal edges. Black cells with a 0 cannot have any adjacent triangles.
• White Rectangles: Every single connected white area on the board must form a clean rectangle or square. White regions can never pinch into sharp 45-degree acute corners, T-shapes, or irregular polygons.

Key Deductions:

Wall Bounding: If an edge of a white space hits a wall or black cell at a 45-degree angle, it must either form a 90-degree corner or continue straight to maintain rectangular proportions. Look at clue cells near corners—a 0 clue forces all adjacent cells to be pure white or point away, drastically constraining the board!