The classic number-placement puzzle. Fill the grid so that every row, column, and box contains each digit exactly once.
How to play
Tap an empty cell to select it, then tap a number from the pad below to fill it in. A cell that already contains a given number cannot be changed. Tap the eraser to clear a mistake.
Objective
Fill every cell correctly without repeating any digit in a row, column, or box.
Strategy tips
Naked singles first: scan for any empty cell where only one digit is possible after eliminating what's in its row, column, and box. These are free placements.
Cross-hatching: pick a digit (say, 7) and eliminate every row and column where a 7 already exists. If only one cell remains in a box, that's where 7 goes.
Box-line reduction: if all candidates for a digit in a 3×3 box lie in a single row (or column), eliminate that digit from the rest of that row (or column) outside the box.