Sudoku (Medium)

Medium puzzles open like Easy ones, with singles, but sooner or later the singles run out and you need one step more. Every grid on this page needs at least one technique beyond singles, and none needs more than the ones described here.

Locked candidates come first. If every place a digit can go inside a box lies in a single row, the digit cannot go anywhere else in that row outside the box: a pointing pair or triple. It works the other way too. When a row's only places for a digit all sit inside one box, the rest of that box cannot hold it.

Then come pairs. When two cells in a row, column or box can only hold the same two digits, those digits must go in those two cells, so you can cross them off everywhere else in the unit: a naked pair. A hidden pair is the mirror image, two digits that can only go in the same two cells, which then can hold nothing else.

This is the level where notes start to pay off. Pencil in candidates for a crowded box or line and look for two cells showing the same pair. Every digit you place clears itself from the notes of the cells it sees, so the patterns surface as you go.

Medium is also the level of the daily puzzle on the main Sudoku page, so a few grids here are the best warm-up for today's ranked time. Puzzles on this page aren't ranked, and their progress is saved separately in this browser.