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- Sudoku
Game rules
Sudoku rules
Sudoku is a puzzle on a 9 by 9 grid divided into nine 3 by 3 boxes. You fill in the digits 1 to 9 so that each appears exactly once in every row, every column and every box. There is no maths involved, only logic.
What are the rules of sudoku?
There are three rules. Every row contains the digits 1 to 9 exactly once. Every column contains them exactly once. Each of the nine 3 by 3 boxes contains them exactly once too. The starting digits stay where they are, and you fill in the empty squares. A well made sudoku has exactly one solution.
Do you need to be good at maths for sudoku?
No. The digits are only symbols here: letters or colours would work just as well. Nothing is added or multiplied; all that matters is that each symbol appears once in every row, column and box.
How do you start solving a sudoku?
Take the digit that appears most often on the grid and look at the boxes that still miss it. Rows and columns that already hold that digit rule out more squares, so often only one square is left in the box. This is scanning, the first and most important technique.
- Naked single: a square where only one digit still fits, because all the others already appear in its row, column or box.
- Hidden single: a digit that fits in only one square of a row, column or box, even though that square has other candidates too.
What should you do when you get stuck in sudoku?
Write small pencil marks in the empty squares: the digits that can still go there. Then look for two squares in the same row, column or box with the same pair of candidates: those two digits must go exactly there, so you can remove them from the other squares of that group. Do not guess. A good sudoku can always be finished by logic, and guessing ends with hunting for a mistake across the whole grid.
What levels does sudoku on klyo have?
Six: Easy (40 given squares), Medium (34), Hard (29), Expert (26), Master (24) and Extreme (22). The level comes from the technique the grid really needs, not only from the number of empty squares. There is also a daily sudoku: one grid for every player for the whole day. When you get stuck, the hint shows the next logical step instead of the finished digit.
Play Sudoku for free
You know the rules, now play. Sudoku runs free in your browser, on a phone and a computer, with nothing to install and no account.