Essential Sudoku Solving Strategies: From Crosshatching to Hidden Pairs

Sudoku is one of the world's most enduring number puzzles. Although it is played with digits 1 through 9, it involves zero arithmetic — it is pure constraint-satisfaction logic.

Whether you are just starting out or looking to tackle hard-level boards, here are key strategies to elevate your gameplay:

1. Crosshatching (Scanning Rows and Columns) The foundational technique for beginners: - Pick a digit (e.g., 1) and scan rows and columns in adjacent 3×3 boxes. - Since a digit can appear only once per row and column, draw imaginary lines through rows and columns that already contain that digit. - Identify the single remaining cell in the target 3×3 box where the digit must reside.

2. Naked Singles A "Naked Single" occurs when an empty cell has only one possible candidate remaining after checking its row, column, and 3×3 box. Always fill Naked Singles immediately.

3. Hidden Singles A "Hidden Single" occurs when a cell has multiple candidate options, but one specific digit has only one legal cell it can occupy within an entire row, column, or block.

4. Naked Pairs & Triples (Intermediate) If two cells in the same row, column, or box can only contain the exact same two candidate numbers (e.g., [3, 7]), those two numbers are locked into those two cells. You can safely eliminate 3 and 7 as candidates from all other cells in that unit.

5. Pointing Pairs (Advanced) When a candidate number in a 3×3 box is confined to a single row or column within that box, that candidate must be placed in one of those cells. Therefore, you can eliminate that candidate from the rest of that row or column outside the box.