How to Play Sudoku: Rules and Solving Techniques
Sudoku is a logic puzzle played on a 9×9 grid divided into nine 3×3 boxes. Some squares start with numbers already filled in. Your job is to fill every empty square with a digit from 1 to 9 so that each row, each column and each 3×3 box contains every digit exactly once. No math is needed, only logic, and every puzzle has exactly one solution.
Solving techniques
- Scanning: pick a digit and look at where it already appears. Each appearance rules out its whole row, column and box. Often only one square is left in a box for that digit.
- Single candidate: look at one empty square and list which digits are still possible. If only one digit fits, write it in.
- Hidden single: sometimes a digit can only go in one square of a row, column or box, even if that square has other candidates too.
- Pencil marks: use Notes mode to jot small candidate numbers in squares. It makes harder patterns visible.
- Naked pairs: if two squares in the same row, column or box can only be the same two digits, those digits can be removed from every other square in that unit.
- Check as you go: Royal Duels highlights conflicting numbers in red so you can catch mistakes early.
A bit of history
The modern sudoku was created by Howard Garns and first published in American puzzle magazines in 1979 under the name "Number Place". A Japanese puzzle company, Nikoli, made it popular in Japan in the 1980s and gave it the name sudoku, roughly "single number". It became a worldwide craze in the mid-2000s when newspapers started printing it daily.
The daily sudoku on Royal Duels
Every day there are three new puzzles: Easy, Medium and Hard. Everyone gets the same puzzles, so you can compare times with friends. Solving them earns 1, 2 and 3 points. You can also play unlimited practice puzzles for fun. On a computer you can type numbers with the keyboard, use the arrow keys to move and press N to switch notes on and off.
More: How to Solve Hard Sudoku