Guides · Sudoku · 9 min read · 2 October 2026

Sudoku solving techniques, from singles to X-Wing

Almost every Sudoku you will meet can be solved with five or six techniques. The trick is not knowing dozens of named patterns; it is knowing which few to look for, and in what order. This guide goes from the ones you use on every move to the one that unlocks most “impossible” hard boards.

Candidates: the vocabulary

A candidate is a digit that could still go in an empty cell: it is not already in that cell's row, column or 3×3 box. Every technique below is just a way of crossing candidates out until one is left. On easy boards you can keep them in your head. On medium and hard, use pencil marks - on Lynxy, switch Notes on and tap digits into the cell.

1. Naked single

A cell where eight of the nine digits are already present in its row, column and box. Only one candidate is left, so that is the answer. Easy boards are mostly naked singles, and they are the first thing to check after every digit you place, because each new digit removes candidates from 20 other cells.

2. Hidden single

Turn the question around: instead of asking which digits fit a cell, ask where a digit fits in a row, column or box. If a 7 can go in only one cell of a box, it goes there - even if that cell has other candidates too.

Hidden singles are the most underused technique among beginners. A good habit: pick a digit, scan the whole board for it box by box, then move to the next digit. It sounds slow, but a full sweep takes under a minute and finds things that cell-by-cell checking misses.

3. Pointing pair

Sometimes a digit's candidates inside a box all sit on one row (or one column). You do not know which of those cells is right yet, but you know the digit is in that row within that box - so it cannot appear anywhere else in that row. Cross it off in the other two boxes along the row.

This is where pencil marks start paying for themselves. The pointing pair rarely places a digit directly; it removes a candidate somewhere else, which often turns a neighbouring cell into a naked single.

4. Naked pair

Two cells in the same row, column or box that both have exactly the same two candidates - say {3, 8}. One of them is the 3 and the other is the 8; you do not know which, but it does not matter. No other cell in that unit can be a 3 or an 8, so cross them out everywhere else in it.

The same logic extends to three cells sharing three candidates (a naked triple), and to the mirror image: if two digits can go in only two cells of a unit, those cells hold those digits, and their other candidates can go (a hidden pair). Naked pairs are by far the most common of these, so look for them first.

5. X-Wing

The X-Wing is the technique that separates “stuck” from “solved” on many hard boards. Pick one digit and look at its candidates in two rows. If, in both rows, the digit can go in exactly two cells - and those cells are in the same two columns - you have an X-Wing.

Why it works: the 5 in row 3 is in column 2 or column 7. If it is in column 2, then row 7's 5 must be in column 7 (it cannot share column 2). If it is in column 7, row 7's 5 is in column 2. Either way, both columns are covered, so no other cell in those columns can be a 5. The same works with columns and rows swapped.

X-Wings are hard to see without pencil marks, and easy to see with them. When a hard board stalls, go digit by digit and look for rows where that digit has only two candidates. Two such rows lining up is less rare than you would expect.

An order that works

1. After every digit you place, check its row, column and box for new naked singles.
2. When that dries up, sweep digit by digit for hidden singles.
3. Fill in pencil marks for the whole board - all of them, carefully. Mistakes here are the main source of “impossible” positions.
4. Look for pointing pairs and naked pairs, then go back to step 1.
5. Only when all of that is exhausted, hunt for X-Wings.

Every board on Lynxy has exactly one solution (we explain how in How a Sudoku with exactly one solution is made), so if none of these steps helps, a candidate has been crossed out by mistake. Going back over the pencil marks of the last box you worked on usually finds it faster than starting over.