Nudoku

This is a Sudoku that can be played with different types of numbers, emojis, drawings or colours. Games can be imported and exported, and a free filling mode allows to set up a game manually. Notes can be used to show which values may match in a position. To solve the puzzle, you have to fill all cells so that in each row, column, and quadratic block of 9 cells each of the 9 symbols appears exactly once. The game offers 4 difficulty levels from easy (around 30 positions left filled) to highest difficulty level with normally around 21 positions left filled. As an additional feature there is a chinese character training mode, which presents the thousand characters of the classical Qianziwen primer in simplified and traditional characters in 125 verses of 8 characters plus the verse number in simple chinese numerals, complete with pinyin transscription, english translation and voice reading the characters. The game offers downloadable illustrations to vary the design. More designs will follow. The hint button either shows errors in already filled cells or, if everything is correct, offers one new correct filling. The note edit button in the middle toggles the note edit mode. With this, instead of the value of the cell possible candidates can be selected that are then shown in a grid inside the cell. Notes that are or become infeasible will be suppressed in the display. In the free filling mode, all cell notes can be activated per menu at once to compose a complete game setup. If any of the note displays become empty, no solution is left. The game will have a single solution when all remaining notes show a single option. In free fill mode, the hint button also checks if a board with a single solution has been reached. In this case, the background turns green and the play button is activated to turn the free fill board into a normal game. Both free filled boards and normal games can be saved. loaded and shared. When a following game cannot immediately be presented after finishing one, for example due to a change in the game level, the game shows a status bar that indicates where across the 81 positions the current iteration starts to look for a solution. Since a game is only valid if there is one single solution possible, it has to retry when more than one solution is found. Normally this is done in the background while playing, but occasionally under some circumstances it will show. The game will play a a couple of notes every second with a pitch from a curated scale that indicates in which of the 9 blocks the current iteration starts. When the music stops that normally means that a single solution is near because the current iteration is not being aborted. Setting up a Sudoku game is a mathematically interesting problem. The more interesting a game setup gets, that is, the less cells are left filled while still having a single solution, the longer it takes to verify this. On the other hand, fewer cells left filled do not guarantee a more difficult path to the solution.