Medium Sudoku

What changes at medium

A medium board still opens easily. The difference shows up in the middle of the solve: you will reach a point where no single row, column or box forces a digit on its own, and progress depends on combining two of them.

This is the level pencil marks were invented for. Once you note which digits a cell could still hold, patterns start appearing that scanning cannot see — two cells in a box sharing the same two candidates, or a digit whose only remaining homes in a box sit in one row.

Most people who describe themselves as regular Sudoku players are playing at roughly this level. It is long enough to feel like a solve and short enough to finish on a commute.

How to solve a medium board

Scan first anyway. Everything that falls out of a plain scan is free, and doing it before you write candidates saves you writing most of them.

When the scan dries up, fill candidates into one box at a time rather than the whole grid — a full grid of pencil marks is slower to read than it is to produce. Look for naked pairs inside the box you just marked up, and for digits with only one home left in the box.

The technique that unlocks the most medium boards is the hidden single: not "this cell can only be a 4" but "the 4 in this box can only go here". They are easy to miss because the cell usually looks like it has several options.

Every board has exactly one solution

Boards here are carved a cell at a time, and any cell whose removal would leave the grid with two valid answers is put straight back. That is what makes the 36-ish clue count on this page a difficulty rather than a gamble: there is always a deduction available, so you never have to guess and back out.

If you cannot find the next move, the honest fix is a technique rather than a hint. The techniques index covers them in the order they start paying off — or paste the grid into the solver and ask for one digit rather than the whole answer.