Sudoku Articles

Practical guides for solving, practicing, and understanding Sudoku puzzles.

Aug 4, 2026

Sudoku Technique: Siamese Fish

Learn how two overlapping fish patterns can combine to remove candidates. This practical guide explains the siamese fish sudoku technique, when to look for it, and a clear candidate-grid example you can use while penciling.

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Sudoku strategy topics

Use these focused guides alongside the articles when you want to practice a specific solving pattern.

Naked Singles Sudoku Strategy A naked single is an empty cell with only one legal candidate left after checking its row, column, and box. Hidden Singles Sudoku Strategy A hidden single appears when a digit can only fit in one cell within a row, column, or box, even if that cell has several candidates. Naked Pairs Sudoku Strategy A naked pair is two cells in the same unit that contain the exact same two candidates, locking those two digits into those cells. Pointing Pairs Sudoku Strategy A pointing pair or triple happens when every possible location for a digit inside a box lies on the same row or column. X-Wing Sudoku Strategy An X-Wing locks a candidate into the same two columns across two rows, or the same two rows across two columns. Y-Wing Sudoku Strategy A Y-Wing uses one pivot cell and two wing cells to prove that a shared candidate cannot appear in cells that see both wings. Swordfish Sudoku Strategy Swordfish extends X-Wing to three rows and three columns, locking a candidate into a larger line pattern.