Skyscraper
Short answer: a skyscraper is an X-Wing that did not quite line up. Two rows each hold one shape in exactly two cells, but the cells share only one column instead of two. The two cells that do not share — the roof — are the point: one of them must hold the shape, so any cell seeing both of them cannot.
What a skyscraper looks like
Look for a failed X-Wing. You find two rows where a shape has exactly two homes each, check the columns, and they only half match — one column is shared, the other two are different. That is not a dead end, it is a skyscraper, and it eliminates just as reliably.
The reasoning runs through the shared column. It can hold the shape only once, so at most one of the two cells in it is real — which means at least one of the two roof cells must be. Anything that sees both roofs is therefore ruled out.
How to use a skyscraper
- Find two strong pairs. Pick one shape and find two rows where it has exactly two possible cells. This is the same first move as an X-Wing, so do both searches at once.
- Check for exactly one shared column. Two shared columns is an X-Wing. Zero shared columns proves nothing. Exactly one shared column is a skyscraper — the other two cells are the roof.
- Check the roofs are in different boxes. If the two roof cells sit in the same box, the pattern collapses into a simple locked-candidate elimination you could have found earlier. It is only worth calling a skyscraper when they do not.
- Strike anything seeing both roofs. Remove the shape from every cell that shares a row, column or box with both roof cells. There are usually one or two such cells, and they are often nowhere near the pattern.
Skyscrapers work in the other orientation too: two columns whose pairs share one row, with the roof running horizontally. As with the X-Wing, scanning only one direction means missing half of them.
Skyscraper vs X-Wing
They start identically — one shape, two rows, two cells each — and differ only in how many columns the pairs share. Two shared columns closes the rectangle and gives you an X-Wing, which clears both columns. One shared column leaves the roof hanging, and you clear whatever sees both roof cells instead. Because the X-Wing search finds skyscrapers for free, it is worth treating them as one habit rather than two: whenever two rows nearly line up, ask which of the two you are looking at.
Find Skyscraper in your own grid
Paste a puzzle and this page will look for Skyscraper in it — the same pattern shown above, in your grid instead of ours. Nothing is uploaded; it runs in your browser.
Frequently asked questions
Why is it called a skyscraper?
Draw the two pairs as vertical lines and the shared column makes them look like two towers of different heights standing on the same ground. The roof is the pair of tops that do not line up — which is also where the elimination comes from, so the name is a useful reminder of what to look at.
How is this different from a turbot fish?
A skyscraper is one specific turbot fish. The general pattern is two strong links joined by a weak one, and depending on whether the links are rows, columns or boxes you get a skyscraper, a two-string kite, or an empty rectangle. Most solvers learn them as separate shapes because they look different on the grid, even though the logic underneath is one argument.
What if the two roof cells see each other?
Then one of them is immediately eliminated, which is a stronger result than the skyscraper itself. If they share a row, column or box, use that directly rather than hunting for cells that see both.
Do I need pencil marks for this?
You need to know where the shape can go in each row, which in practice means keeping candidates for that shape at least. Full pencil marks make it far easier, though: skyscrapers depend on counting to exactly two, and eyeballing that reliably across a whole grid is much harder than reading it.