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TODAY'S CHALLENGE
The rules
How do you play Sudoku?
Sudoku is a logic puzzle where the goal is to fill a 9×9 grid with the numbers from 1 to 9. You need no math skills - it's all about logic and a little patience. Four simple rules are all it takes. Click a rule, and the board shows you exactly what it means.
Fill the grid
- A sudoku board has 9×9 cells, and some numbers are filled in beforehand. These are your clues. The goal is to fill each empty cell with a number from 1 to 9, using only logic.
- Each horizontal row must eventually contain all the numbers from 1 to 9. Each number must appear exactly once, neither more nor less.
- In the same way, each vertical column must contain all the numbers from 1 to 9. Each number can only appear once.
- The board is also divided into nine boxes of 3×3 cells. Each box must also contain the numbers from 1 to 9, once each. These three rules apply at the same time all the time.
Each row 1 to 9
- The goal is to fill the row with all the numbers from 1 to 9. Each number must appear exactly once.
- The number 9 is already in this row. If we place 9 once more, we get two of the same. Then there won't be room for all the other numbers, which is why it's not allowed.
Each column 1 to 9
- The goal is to fill the column with all the numbers from 1 to 9. Each number must appear exactly once.
- The number 7 already exists in this column. Each number can only appear once, otherwise not all nine numbers will fit. That's why 7 can't go here.
Each box 1 to 9
- The goal is to fill the box with all the numbers from 1 to 9. Each number must appear exactly once.
- The number 9 is already used in this box. Since each number must only appear there once, a new 9 would become a duplicate. That's why it's not allowed.
Strategy
How to improve your skills?
Three techniques take you from guessing to pure logic. Choose a technique and flip through the steps. The board shows what happens.
Naked single
A naked single is a cell that has only one possible number left. It's the simplest technique, and it's perfect to start with.
- We look at the highlighted cell. To find the number that fits, we check the row, column and box it's in.
- First we write in all the numbers from 1 to 9 as candidates. Then we can see which of them are actually possible.
- The numbers 1, 2, 3, 4, 6, 7, 8 and 9 already exist in the row, column or box. Because a number can only appear once, we cross them out.
- Then only 5 is left. Because all the other numbers are excluded, 5 must go here. This is what we call a naked single.
Candidate notes
When you note which numbers are possible in each cell, both naked and hidden singles become much easier to see.
- When you're unsure what goes in a cell, you can write small numbers in the corner. These are called candidate notes.
- We write in all the numbers that are still possible in each cell. Then we can quickly see which cells have only one number left, and which numbers only fit in one place.
Daily habit
Why play sudoku daily?
A daily Sudoku routine gives both mental energy and small breaks in everyday life. Many use the boards as a morning ritual or as a break at work. Here are the benefits:
Strengthens the brain
Playing Sudoku stimulates the brain and trains both working memory and mental flexibility. It's brain training at its best!
Increases focus
Sudoku requires concentration. With daily training you'll notice that your focus lasts longer - also outside the game.
Improves problem solving
Regular problem solving gives you better strategic understanding and makes it easier to think critically and in a structured way.
Questions and answers
What people wonder about
Wondering how today's challenge, difficulty levels or accounts work? We've gathered answers to the most common questions in one place.
See all questions and answersEverything about rules, today's challenge, account and more
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