數獨 (Sudoku) is a logic-based, combinatorial number-placement puzzle. The objective is to fill a 9x9 grid with digits so that each column, each row, and each of the nine 3x3 sub-grids that compose the grid contains all of the digits from 1 to 9.


FEATURES:
- four different difficulties
- hundreds of puzzles for each difficulty
- auto-save your progress for each puzzle
- unlimited undo/redo
- auto-fill drafts
- hint system for beginners
- color input system for experts
- clean interface and smooth controls
- google play games achievements
- phones and tablets support

HELPFUL FEATURES (optional):
- selection modes: select first or number first
- pencil modes: automatic or manual
- keyboard configuration: three rows, two rows, one row
- direction highlight: vertical and horizontal highlight
- number finder: highlight all occurrences of a number
- number counter: show a counter for each number
- rule violations: game rule warnings highlight
- keyboard highlight: shown if number count is correct or incorrect
- multiple color input (advanced): use different colors to place numbers
- automatic error detection: show errors automatically
- permanent auto-fill: continuously fill all the drafts
- bigger numbers: large font for better visualization