How to Solve Sudoku: Beginner Techniques That Work
Sudoku looks like a math puzzle, but it needs no arithmetic at all. The numbers 1 to 9 are just symbols, and you solve it with logic. Here is how to get started, and a few techniques that solve most easy and medium puzzles.
The rules
Fill the 9x9 grid so that every row, every column and every 3x3 box contains each of the numbers 1 to 9 exactly once. The numbers already in the grid are fixed.
Technique 1: look for a square that can only be one number
Pick an empty square and check which numbers are already in its row, its column and its box. If eight of the nine numbers are taken, the ninth is the answer. This is called a naked single, and many easy puzzles are solved by repeating it.
Technique 2: look for a number that can only go in one place
Choose a number, say 7, and look at one row, column or box. If 7 is not there yet and only one empty square in it can hold a 7 (the others see a 7 in their row, column or box), then it goes there. This is called a hidden single.
Technique 3: write small notes
When no square is obvious, write the possible numbers in small print in each empty square (pencil marks). As you place numbers, cross out the ones that no longer fit. Patterns start to show, for example two squares in a row that can only hold the same two numbers, which means those two numbers cannot go anywhere else in that row.
Good habits
- Scan rows and columns that are almost full first.
- Work on one number at a time across the whole grid.
- Use a pencil. If you hit a contradiction, one of your last placements was wrong.
- Do not guess. Every puzzle from the generator has exactly one solution that logic can find.
Practice
Start with the 4x4 puzzles if you are new, then move to easy, medium and hard 9x9 puzzles. Every set comes with an answer page to check your work.
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