The Skyscraper strategy is named because it visualizes two tall buildings of different heights standing side-by-side.
It acts like an X-Wing with a "broken" corner. Where an X-Wing forms a perfect rectangle, the Skyscraper has one side shifted up or down, creating an uneven roof.
Interactive Example
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Click "Apply Logic" to see the strategy in action.
Real Example Explanation
In the interactive example above, look at the number 3:
- The Base: Look at Row 1 (the ground floor).
- The candidate 3 appears only twice: at R1C3 and R1C4.
- This is our solid foundation. We know that one of these two cells must contain a 3.
- The Towers:
- Tower A (Left): R1C3 connects to R9C3. This is a 9-story tower.
- Tower B (Right): R1C4 connects to R8C4. This is an 8-story tower.
- Because the tops (R9C3 and R8C4) are in different rows, we have a Skyscraper.
- The "One-Two Punch" Logic:
- Since our Base (Row 1) must have a 3, it forces a choice:
- Option 1: R1C3 is the 3. Then the Left Tower is "active".
- Option 2: R1C4 is the 3. Then the Right Tower is "active" (pushing the valid 3 to R8C4).
- The Result: It is impossible for both tower tops to be empty. One of them (R9C3 or R8C4) must contain a 3.
- The "Kill Zone" (Elimination):
- Since at least one top is real, any cell that can see BOTH tops cannot be a 3.
- The Red cells (e.g., R8C2, R9C5) fall into this crossfire and can be cleared.
How to Spot It
- Pick a Number: Scan the grid for a number (like 3).
- Find Two Columns: Look for two columns where that number appears exactly twice.
- Check the Base: Two of these spots must be in the same row (the floor).
- Check the Roof: The other two spots must be in different rows (the uneven roof).
- Eliminate: Find the intersection cells that see both roof tips.
Quick Comparison
- X-Wing: Two Columns, Two Rows. Perfect rectangle.
- Skyscraper: Two Columns, Three Rows. Rectangle with a shifted corner.
Related Strategies
- X-Wing (Col): The perfect version.
- 2-String Kite: Another variation of the Turbot Fish.