X-Wing Sudoku: technique, search method and quiz

You can solve easy Sudokus, but hard puzzles always leave you stuck on the same cells? You pencil in all the candidates and nothing moves forward? X-Wing is very likely the technique you are missing.

The X-Wing is one of the first advanced techniques to master in order to move from intermediate to expert level. In this tutorial, I explain everything: the technique on rows, on columns, the search method, and an application quiz to check your understanding.

🎬 The full Domino33 video on X-Wing

Before the written content, here is the 15-minute video where I detail the X-Wing in two parts (rows / columns), the search method, and the final quiz. English subtitles available (click ⚙️ on the player):

▶ English subtitles available — click the ⚙️ icon and select English.

The article below follows the same structure as the video so you can learn in your preferred way (reading, video, or both).

Part 1
Row X-Wing & Column X-Wing

What is an X-Wing?

An X-Wing is a candidate elimination technique based on a rectangular pattern. When 4 cells in a grid form a perfect rectangle and all contain the same digit as a candidate — and only in these 4 cells for the 2 rows (or columns) involved — you can eliminate this candidate from the other cells in the columns (or rows) of the rectangle.

The name "X-Wing" comes from the shape drawn by the diagonals connecting the 4 cells: a capital X. The technique exists in two orientations: row X-Wing and column X-Wing.

1️⃣ Row X-Wing (example)

We talk about row X-Wing when we spot the pattern on two rows of the grid. Here is a concrete example with the digit 4 on rows 2 and 6:

The 4 cells circled in red form the X-Wing. The crossed-out "4"s are the candidates to eliminate in columns 3 and 7.

Reading the diagram:

• On row 2, the 4 is only a candidate in columns 3 and 7
• On row 6, the 4 is also only a candidate in columns 3 and 7
• The 4 cells (R2C3, R2C7, R6C3, R6C7) form a perfect rectangle

Logic: the 4 will be placed either at R2C3 + R6C7 (diagonal 1), or at R2C7 + R6C3 (diagonal 2). In both cases, the 4 will occupy one cell in each column of the rectangle. So we can eliminate all other 4 candidates in columns 3 and 7 — here at R4C3, R4C7, R8C3 and R8C7.

2️⃣ Column X-Wing (example)

The column X-Wing is the "rotated 90°" version: the pattern is spotted on two columns and allows elimination in the rows of the rectangle.

Concretely: on 2 columns, the same digit has only 2 candidate cells, located on the same 2 rows. We get a rectangle, and we can eliminate this digit from all other cells in the 2 rows of the rectangle.

In my video, I show both orientations with different grids so you can clearly see the visual difference between the two.

Part 2
The X-Wing search method

Now that you know what an X-Wing is, you still need to know how to spot it quickly in a grid. Here is the Domino33 method in 4 steps:

Step 1 — Choose a digit to analyze

No need to search everywhere at once: your brain will get lost. Focus on one digit at a time (the 1, then the 2, etc.). Do this for each digit still to be placed in the grid.

Step 2 — Spot the "binary" rows for this digit

A row is called "binary" for a digit when this digit has only 2 candidate cells left on this row (no more, no less). This is the only configuration that can produce an X-Wing.

Step 3 — Look for a second aligned binary row

Once a binary row is found, scan the rest of the grid to find another row where this same digit is a candidate in exactly the same two columns. If you find it: you have a row X-Wing.

Step 4 — Repeat the work on columns

Once the rows are scanned, repeat the same search on the columns. Many beginners miss an X-Wing because they only think of one orientation.

Part 3
Application quiz

Now that you have seen everything — theory, row and column examples, and the search method — it is time to put it all into practice. Here is a mini-quiz to check your knowledge. Good luck!

❓ Frequently asked questions

📋 In summary

As with cycling, it is through practice that you become able to spot X-Wings in seconds. To practice, download free level 6+ puzzles from the Domino33 site or subscribe to the channel to discover other advanced techniques.