Medium Sudoku

If easy puzzles feel too quick and hard ones feel punishing, this is the level to settle into.

How medium puzzles differ from easy ones

Medium puzzles here start with roughly 32 to 36 givens. That is enough to begin without guessing, but not enough to finish by looking at one square at a time. Many squares will have two or three candidates for a while, and you will need to find the places where those candidates give each other away.

The rules never change: every row, column and 3 by 3 box holds the digits 1 to 9 exactly once. What changes is how much you must keep in your head, which is why good pencil notes matter.

Make pencil notes work for you

Once you have placed every single you can find, switch on Notes and fill in the candidates for the empty squares. This takes a few minutes but turns the puzzle into something you can read. When you enter a number, the game clears it from the notes in its row, column and box, so you do not have to.

Fill candidates in a region at a time, starting with the rows, columns or boxes that are most complete. A tidy set of notes shows patterns that are invisible on a bare grid.

Techniques you will meet

Naked pairs

If two squares in the same row, column or box both contain only the same two candidates, say 3 and 8, then those two digits must go in those two squares. You can erase 3 and 8 from every other square in that region.

Hidden pairs

Sometimes two digits appear in only two squares of a region, alongside other candidates. Those squares must hold that pair, so you can remove their other candidates.

Pointing pairs and triples

If a digit's candidates inside a box all lie in one row or column, that digit cannot appear anywhere else in that row or column. Erase it from the rest of the line.

Box and line reduction

The reverse also works. If a digit in a row or column can only go in squares that sit inside one box, it cannot appear in any other square of that box.

A step-by-step approach

1. Place every hidden and naked single you can see.
2. Add notes to the remaining squares, one box or row at a time.
3. Look for pairs and triples of identical candidates and use them to clear other squares.
4. Look for pointing pairs where a digit is confined to one line inside a box.
5. After each elimination, check for new singles. Elimination and placement feed each other.
6. If you are stuck, scan a different digit or a different region before reaching for a hint.

Tips for faster solving

• Focus on the digit that appears most often. It has the fewest remaining places.
• Use the highlight feature: tap a number on the grid and every matching digit lights up, making conflicts obvious.
• Check the most crowded rows and boxes first. They are likely to be one step from completion.
• Work in short bursts. A break often reveals a move you could not see before.
• Use the Hint button once to learn where you were missing a technique, rather than for the answer.

Why people play sudoku

Sudoku exercises working memory, patience and pattern recognition, and many people enjoy it as a calm daily habit. It is not a medical treatment, but a puzzle after lunch or before bed is a pleasant way to switch off. The puzzle itself is generally credited to the American Howard Garns and was first published in 1979. It was then popularised in Japan in the 1980s and spread worldwide in the 2000s.

Common questions