What makes a puzzle medium here
A medium puzzle on this site needs at least one technique beyond naked singles, and never anything harder than the five listed below. Our solver works through every puzzle before it is published and records which techniques it had to use. If naked singles were enough, the puzzle is filed under easy. If it needed an X-Wing or anything more advanced, it is filed under hard. Medium sits in between, and it is checked for exactly one solution like everything else here.
Many medium puzzles turn on a few hidden singles and nothing else. Others need a pair or a box-line elimination at the tightest point. You will not know which until you get there.
The five techniques you may need
- Hidden single. A digit that can go in only one square of a row, column or box, even though that square still has other candidates. Scan for the digit, not the square.
- Naked pair. Two squares in the same unit that share the same two candidates and nothing else. Those two digits can be removed from every other square in that unit.
- Hidden pair. Two digits that can only go in the same two squares of a unit. Those squares cannot hold anything else.
- Pointing pairs and triples. Inside a box, a digit’s candidates all sit in one row or column. The digit can be removed from the rest of that row or column outside the box.
- Box-line reduction. The reverse: in a row or column, a digit’s candidates all fall inside one box, so it can be removed from the rest of that box.
Expect to use pencil marks at least in the tighter corners of the grid.
Who these are for
Medium is the right level if you finish easy puzzles without effort and want something that takes a coffee break rather than a minute. It is the level most newspaper regulars live at. It also suits anyone learning the techniques above, because every puzzle here is guaranteed to be solvable with them. When you get stuck, the way forward is either a single you missed or one of the five patterns above.
Printing tips
Pencil marks need space. If you write candidates in the corners of squares, choose two per page, or one per page for large print. Four per page works fine if you keep the marks in your head. The answer key prints on the last page; untick Include answers if you would rather not have it.
Other levels
Too easy? Try hard sudoku. Too hard? The easy page is a good place to warm up. The daily sudoku is medium from Wednesday to Friday.