Currently this is the best version of cross sums/karuko/sum totals on the iOS App Store to my knowledge, some issue's I would like to see addressed in the future are:
1) largest sized puzzles take to long to generate due to the brute force method being employed, you can begin calculating a new game in the background as soon as the game has begun so that there is always at least one new game instantly ready.
2) menu system needs a complete redesign, i do not need a full time restart button or new game button, lets use that screen real estate more wisely. for instance
3) undo needs to be able to undo constraint changes not just final choices - it is very useful to have these as two seperate buttons and undo stacks.
3.5) user entered constraints need to be removed as you fill in final values (be sure to include group these implicit changes in the undo stack so that they undo if the final choice that caused them is undone).
4) smart autocomplete can be implemented without ruining the game but take away the tedious drudge work - start simple and just fill in remaining single digits - ie 24 = 7 8 9, and i have 7 and 9 filled in, please auto complete the 8 and add it to the undo stack. in theory this could be taken further and you could cascade autocomplete until there are no more 'trivial case' solutions. autocomplete should stop upon logical errors obviously (this is when implementing undo properly really matters)
5) bigger game grids on ipad would be nice.
6) timer need not start until player places first digit (at least as long as new game generation takes more than a fraction of a second), at the end of a game it should be one tap to start a new game with the same options (redo the non playing UI to get rid of tiny text menus and the like and go with a more custom game/karuko centric UI)
7) be nice to have a built in tool to calculate difference between a set of rows and a set of columns of remaining unknown digits - ie double tap header to include in column and/or row sum say then just update the result etc (this is kind of advanced but simplifies solving expert level puzzles for skilled players but coming up with a simple UI for it should make it intuitive to use)
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