QuietdokuHow to play sudoku
Sudoku takes a minute to learn and a lifetime to master. Here are the rules and the first techniques you need.
The rules
- The board is a 9×9 grid divided into nine 3×3 boxes.
- Fill every empty cell with a digit from 1 to 9.
- Each row, each column and each 3×3 box must contain every digit exactly once.
That’s all. There is no math involved — the digits could just as well be letters or colors. A well-made puzzle has exactly one solution and can be solved by logic alone.
Techniques, from first steps to expert
Naked single
A cell where eight of the nine digits already appear in its row, column or box. Only one digit can go there.
Hidden single
Inside a row, column or box, a digit that fits in only one cell — even if that cell has other candidates.
Pencil marks
Write the possible digits (candidates) in small numbers. Most harder techniques work by eliminating candidates.
Locked candidates
If a digit’s candidates in a box all sit in one row, that digit can be removed from the rest of that row.
Naked and hidden pairs
Two cells in a unit that can only hold the same two digits. Those digits can be removed from the other cells of the unit.
X-Wing
A digit that appears as a candidate in exactly two cells of two rows, lined up in the same two columns. It can be removed from the rest of those columns.
Tips for getting unstuck
- Scan one digit at a time across the whole board before switching to the next.
- Start with the most crowded rows, columns and boxes.
- When you use pencil marks, update them every time you place a digit.
- Take a short break. A fresh look often finds what a long stare misses.