Sudoku Tips for Beginners: How to Solve Any Puzzle Without Guessing
A sudoku grid can look intimidating, but it needs no maths and no guessing. The numbers are just symbols, so the puzzle would work just as well with nine different colours. Every proper sudoku has one solution that you can reach through logic alone. Once you know a few techniques, you can start to see moves that once felt impossible.
The rules
The grid has nine rows, nine columns and nine 3×3 boxes. Some cells are already filled in. Your job is to fill in the rest so that each row, column and box contains the numbers 1 to 9 exactly once. That is all there is to it.
The name comes from a Japanese phrase meaning roughly "the digits must be single". The puzzle spread worldwide in 2005, after newspapers started printing it.
Technique 1: scanning
This is where every solve should begin. Pick a number that already appears several times, say 7. Look at each box that does not contain a 7, and use the 7s in nearby rows and columns to rule out cells. If only one cell in a box is left, the 7 goes there.
Work through all the numbers from 1 to 9. On easy puzzles, scanning alone may be enough.
Technique 2: the only number left
Now look at it from the point of view of a single cell. Check the row, column and box it belongs to, and cross off every number already there. If only one number remains, you have your answer. This is known as a naked single.
A good place to look is any row, column or box with only two or three empty cells.
Technique 3: pencil marks
When scanning stops working, write the possible numbers in small print in each empty cell. Most sudoku games have a notes mode for this. It takes a little time, but it reveals patterns you cannot see otherwise, and it means you never need to guess.
Update your notes each time you place a number. Every placement removes that number from the other cells in the same row, column and box.
Three patterns for harder puzzles
Hidden single
A cell may have several candidates, but if one number appears as a candidate in only one cell of a row, column or box, it must go there. These are easy to miss, so check for them whenever you get stuck.
Naked pairs
If two cells in the same row, column or box both contain only the same two candidates, say 3 and 8, then those two numbers must go in those two cells. You can cross 3 and 8 off the rest of that group, which often unlocks other moves.
Pointing pairs
If a candidate in a box appears only in a single row, it must go in that row within that box. That means you can remove it from the rest of the row outside the box.
When you get stuck
- Go through each number from 1 to 9 again. It is easy to miss something simple.
- Check your notes for mistakes. One wrong note can hide a solution.
- Look for hidden singles in rows and columns, and not just in boxes.
- Step away for a few minutes. A fresh look often shows the next move right away.
Common mistakes
- Guessing. A wrong guess can stay hidden for a long time, and it is painful to untangle.
- Forgetting to update notes. Out-of-date notes will lead you to wrong conclusions.
- Starting on Insane. Work up through the levels, so that you learn each technique when you need it.
A daily habit
Many people enjoy a sudoku with their morning coffee. Start on Easy mode until scanning feels natural, then move up. If you enjoy number puzzles, try 2048 Legend as well, which trades careful logic for quick decisions.
