Three rules you need to remember
Must contain all digits 1–9 with no repeats.
It must also contain the digits 1–9 exactly once.
The nine cells in a block cannot contain duplicate digits.
How to solve a Sudoku puzzle step by step
- 1
Find a nearly complete row, column, or block
Start where only a few cells are empty. The missing digits are easier to spot there.
- 2
List the missing digits
For example, if a row already contains 1, 2, 4, 5, 6, 8, and 9, only 3 and 7 remain to place.
- 3
Eliminate using the column and block
For each empty cell, check which digits already appear in its column and 3×3 block. If only one choice remains, you have a forced move.
- 4
Repeat after every new digit
A newly placed digit can open the next step in another row, column, or block.
When should you write candidates?
When a cell has two or more possibilities, do not guess. Write the possible digits as Notes. As other eliminations happen, the candidate list will gradually shrink.
Six techniques to learn in order
A cell has exactly one valid candidate left.
A digit can appear in only one cell in a row, column, or block.
When a candidate in a block is restricted to one row/column—or vice versa—you can eliminate that candidate from the rest of the intersection.
Two cells contain exactly the same two candidates, allowing those candidates to be removed from other cells in the same region.
Two digits can only occupy the same two cells, so other candidates can be removed from those two cells.
A candidate appears in exactly the same two positions across two rows or two columns, forming a pattern that lets you eliminate that candidate from the other intersecting positions.
Three habits that slow down your solving
- Staring at one area too long instead of moving to another row/column when stuck.
- Adding too many candidates and failing to update them after entering a new digit.
- Guess a digit to “test” it, then continue from an unproven assumption.
Which difficulty should you choose?
Finished reading? Apply it now.
Start with an Easy or Medium game and focus on certain moves before using hints.