SudokuPlay is a simple platform for playing Sudoku. Players can get rated games, generate new, unrated games, use the iPhone camera to create games from paper copies and screenshots, share games using Copy/Paste, or enter games manually. From the Manual play window swiping right shows the automated version of the game (Auto), swiping left from Manual goes to the Markup version of the game. Changes are made to the 9x9 Sudoku cells using the standard iPhone text field editor.

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Manual mode is where the game is played. Tapping a cell brings up a text box for editing the possibles of the cell. Manual features include Undo, Undo To Checkpoint and Fill Cell Possibles Once, which fills in the possibles as calculated by Auto mode.

 

Auto mode is intended for use when the player has run out of moves. Auto shows, using highlighting and colouring, how possibles can be eliminated from cells using various strategies collected from the broader Sudoku community and implemented in the app. When a cell has been solved, Auto mode removes the cell's value from all other cells in its row, column and square. When cells have more than one possible, Auto and Manual are independent of each other. When a cell is solved it is solved in both Auto and Manual.

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Games can be saved from either Manual or Auto to the Game Selection list where the player can continue with games in progress, rename and delete games. A variation of Save is the Keep feature which stores the game with all of its Undo data intact. 

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The third mode, Markup, can be used to highlight cells and possibles in the cells. In Markup you can practise recognizing and highlighting cells and significant possibles in the cell, that together form the elements of a strategy. You can then mark possibles for deletion from cells that are in the scope of the strategy.

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Characteristics of a SudokuPlay Sudoku:

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1. There is one and only one solution to the game. 

2. Some games are virtually unsolvable. There are few or no moves to make, even using reduction strategies. A player can guess what a cell value is and play till they need to guess again or they solve the game or encounter an error. SudokuPlay facilitates guessing with an "Undo to Checkpoint" feature. However, some puzzles are nearly impossible to solve even with guessing.

3. When generating a new game, SudokuPlay starts with a completed puzzle created randomly, then works backwards, removing cell values and testing the results, until the target number of filled cells is reached. The practical minimum for SudokuPlay is 21 filled cells, out of 81 total cells. If game generation takes too long or fails repeatedly, increasing the number of filled cells helps.

4. In messages produced by the game, cells are numbered 0 to 80, rows, columns and squares are numbered 0 to 8.

5. Rated game difficulty levels range from 1 to 10, with 9 & 10 being Unsolvable. Levels 1 & 2 are Easy, 3 & 4 are Medium, 5 & 6 are Difficult and 7 & 8 are Very Difficult.

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