Sudoku for beginners: three moves that solve most puzzles
You don't need to guess, and you don't need to be good at math. You need these three moves.
A Sudoku grid has 9 rows, 9 columns and nine 3×3 boxes. Fill the empty cells so that each row, column and box holds every digit from 1 to 9 exactly once. There is no arithmetic involved. The digits could just as well be letters.
1. The only number left
Pick an empty cell. Cross off every digit already in its row, its column and its box. If only one digit remains, that is the answer.
2. The only place left
Now turn it around. Pick a digit, say 7, and a box that doesn’t have one yet. Look along the rows and columns that pass through the box. Every 7 you find there rules out a whole line of cells. If only one cell in the box is left, the 7 goes there.
Start with the digits that already appear most often on the board. They rule out the most cells.
3. Notes and pairs
When neither move works, switch on notes and pencil in every digit each cell could still take. Then look for two cells in the same row, column or box that share the same two candidates, such as 3 and 8. One of them is 3 and the other is 8, so no other cell in that row, column or box can be either. Erase those notes, and a new single often appears.
Don’t guess
A well-made Sudoku has exactly one solution, and you can reach it by logic alone. A guess that turns out wrong can spoil several moves before you notice it.