Skyscraper Sudoku Technique: Advanced Pattern Recognition Method - SudokuPuzzles.net
Master the Skyscraper technique in Sudoku, an advanced pattern recognition method that uses strong and weak links to eliminate candidates. Complete guide with examples.
The Skyscraper technique is an advanced Sudoku solving method that uses the concept of strong and weak links to eliminate candidates. It's named for its visual resemblance to skyscrapers when drawn on a Sudoku grid. This powerful technique can help you solve even the most challenging puzzles.
What is the Skyscraper Technique?
The Skyscraper technique is a pattern recognition method that works when a specific digit appears in exactly two cells in two different rows (or columns), and these cells share a common column (or row). The pattern creates a logical chain that allows you to eliminate candidates from other cells.
The technique gets its name from the visual pattern it creates when drawn on the grid - it looks like two skyscrapers connected by a base.
Understanding Strong and Weak Links
Before learning the Skyscraper technique, you need to understand two key concepts:
Strong Link
A strong link exists when a digit can appear in exactly two cells in a row, column, or box. If the digit is not in one cell, it must be in the other.
Weak Link
A weak link exists when a digit can appear in two or more cells in a row, column, or box. If the digit is in one cell, it cannot be in the others.
How the Skyscraper Pattern Works
For a Skyscraper pattern to be valid, you need:
- A specific digit that appears in exactly two cells in two different rows (or columns)
- These two rows (or columns) must share a common column (or row)
- The digit must form a strong link in each row (or column)
- The pattern must create a logical chain for elimination
Step-by-Step Skyscraper Identification
Step 1: Choose a Target Digit
Start by selecting a digit that appears frequently in your puzzle. Look for digits that have candidates in multiple rows and columns.
Step 2: Find Two Rows with Strong Links
Identify two rows where your target digit appears in exactly two cells each. These create strong links.
Step 3: Check for Common Column
Verify that these two rows share exactly one common column where the digit appears.
Step 4: Apply the Elimination
If the pattern is valid, eliminate the target digit from cells in the common column that are not part of the Skyscraper pattern.
Skyscraper Example
Let's say we're looking for digit 7 in a Skyscraper pattern:
Row 2: 7 appears in columns 1 and 5
Row 6: 7 appears in columns 1 and 8
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