SUDOKU WAR

Goal. Fill the 9 × 9 grid so that every row, every column and every 3 × 3 box contains each digit from 1 to 9 exactly once. Every grid has a single solution.

• The digits given at the start are in bold on a grey background: they cannot be changed. Yours are in blue.
• Tap a cell to select it, then tap it again: 1, 2, ... 9, then it becomes empty again.
• Or select the cell, then the digit on the pad. Under each digit: how many are still to be placed.
• Long press (or double click) on a digit of the pad: it stays selected and every cell you tap receives it. Tap it again to release it.
• Notes: the Notes button writes the possible digits of a cell small, in orange (several per cell). A note is hidden when its digit is placed in the same row, column or box, or placed 9 times; it is never lost and comes back if you remove that digit.
• Not here: the Not here button marks in blue, crossed out, a digit you have ruled out for a cell. It is added and removed like a note.
• Help (Beginner and Medium): the Help button shows in green the digits still possible, i.e. those not already in the row, column or box. In Beginner, for every empty cell; in Medium, for the selected cell only, and the time is then not ranked.
• A selected digit flashes everywhere it appears. A selected empty cell highlights its row, its column and its box in mauve.
• Undo, Redo, Erase and, in solo, Pause (the grid is hidden and the timer stops).
• Grid number: every game has its own number, shown under the banner. Copy it to replay exactly the same grid or share it with a friend (Master choice, “Grid no.” field).

Levels. Grids are ranked by the hardest deduction needed to finish them: Beginner, naked and hidden singles; Medium, pairs and box-line alignments; Expert, X-Wing, XY-Wing and simple chains; Master, even more advanced reasoning.

Solo. The timer runs; the grid is checked once it is full. Your game is saved: you can resume it whenever you like. In Beginner, obvious duplicates are shown in red.

Multiplayer. Everyone has the same grid. The warning shows how many cells the leading opponent has left, without ever showing their digits. No mistakes are flagged along the way: only a grid that is full but wrong is announced, without saying where. The first to fill in the grid correctly wins and the game ends for everyone.