Skyscraper Sudoku Rules Explained + 5 Tips & Techniques

Skyscraper Sudoku is a Sudoku variant where additional clues are presented outside of the main grid along the rows and columns. Just like in the example below.

These clues relate to the number of cells ‘visible’ from that particular vantage point if you imagine the cells are all ‘skyscrapers’ with their value indicating how many floors high a particular skyscraper is. 

For example, cells with a value of 3 would be 3 floors high. Cells with a 5 would be slightly taller as their total number of floors would be 5. 

Because every cell along a row or column will have a different value, all the skyscrapers will also be of different heights. This means that some taller skyscrapers will block the view of smaller ones.

To better visualize this, let’s consider the single row of cells in the image below where cells have been transformed into ‘skyscrapers’ with heights based on their value. 

Here you can see if you look along the row from the left, you can also see two ‘skyscrapers’ (the 7 and 9 cells). Whereas if you look from the right, you can see six (the 2, 3, 5, 6, 8, and 9 cells) but you cannot see the 1, 4, or 7 cells as these are obscured by higher values.

Another way to consider this is to think of what it would look like if you were facing this row head-on. This view is shown in the image below. 

Here you can see that only the 7 and 9 ‘skyscrapers’ are the only visible buildings and all the others are hidden behind them. 

Rules

Now that you have an idea of how Skyscraper Sudoku puzzles work and what the numbers outside the grid mean, let’s quickly go over all the rules of Skyscraper Sudoku.

• Normal Sudoku rules still apply (every row, column, and 3×3 box must contain the numbers 1 through 9 exactly once each.
• Additionally, the skyscraper clue is equal to exactly the number of visible skyscrapers along the row or column it corresponds to. That is, there cannot be any more or fewer visible ‘skyscrapers’ as viewed along the row or column.
• Higher ‘skyscrapers’ only block the view of lower ‘skyscrapers’ and not any ‘skyscrapers’ that are even higher regardless of how far along the row or column they are. (E.g., an 8 at one end of a particular row does not block the view of a 9 all the way at the other end. 

Skyscraper Sudoku tips & techniques

Now that you have an understanding of how to solve Skyscraper Sudoku puzzles, here are some tips and techniques worth keeping in mind:

• Any 9 clue means that every skyscraper is visible along that row or column. This means that the cells must be ordered exactly 1, 2, 3, 4, 5, 6, 7, 8, 9. As any other order would mean at least one skyscraper is not visible and therefore you would not be able to see all 9 skyscrapers.
• Any 1 clue means that only one skyscraper is visible and therefore the first cell along the row or column must be a 9. If it was any other number, then not only would the first ‘skyscraper’ be visible but also the 9 and any other taller cells as well.
• Look for high-value clues as these will mean that tall skyscrapers will be forced to the end of the row or column. For example, if you have an 8 clue then the 9 must only be in either of the two last cells along the particular row or column. 
• Consider how different clues along rows and columns interact with each other. In other words, remember that each cell must satisfy any clues gives for both its row and column.
• Don’t forget about the normal rules of Sudoku. Or in skyscraper terms, remember that each building along every row, column, and 3×3 box must be of different heights. 

Where to play

You can find plenty of Skyscraper Sudoku puzzles to play over on Krazydad.