What makes these puzzles hard
An expert grid starts with about 23 givens instead of 30 or more. Singles run out quickly, so you need techniques that remove candidates rather than place digits: naked and hidden pairs, pointing pairs, box-line reduction and sometimes an X-Wing. Every puzzle here is checked to have exactly one solution.
A routine that works
- Place every hidden single you can find first.
- Fill in all candidates for the whole grid (turn on Notes).
- Look for pairs and triples in each row, column and box, then for pointing pairs.
- After every placement, the game clears that digit from notes in the same row, column and box, so new singles appear.
- When nothing moves, look for an X-Wing: one digit with exactly two spots in two rows that line up in the same two columns.
When you’re stuck
Re-check your notes before anything else; one wrong candidate hides every next step. Turn on Show mistakes if you want a safety net. Our sudoku techniques guide explains each method with examples. Need a break? Try the daily sudoku.