Grouped 3 Skyscrapers
Grouped 3 Skyscrapers is a variant of 3 Skyscrapers where at least one of the three strong links is grouped — instead of a digit confined to exactly two cells in a row or column, it's confined to two groups of cells within a single block. The chain still forces at least one of the two roof endpoints to hold the digit, eliminating it from any cell that sees both.
What is a Grouped 3 Skyscrapers?
A regular 3 Skyscrapers needs three parallel rows or columns where a candidate digit appears in exactly two cells per house. Grouped 3 Skyscrapers relaxes that requirement: at least one of the three strong links can be a grouped link, where the digit is confined to two groups of cells inside a single block instead of two individual cells. The other two links stay as ordinary single-cell conjugate pairs. The chain still runs through three parallel houses, the bridge cells still see each other, and the same roof-elimination applies. The only structural difference is that one link's "two cells" are replaced by "two cell groups" within a block — for example, the digit can only sit in the top-left or bottom-right corner of a block.
How to spot it
Scan one digit at a time, looking for three parallel rows or columns where it's restricted to two cells — the same starting point as regular 3 Skyscrapers. But also check each block: if the digit is confined to two groups of cells within a block (not two single cells, but two clusters that can't both hold the digit), that counts as a grouped strong link. When you can chain three such links — two ordinary and one grouped, or any mix — through bridge cells that see each other, you've got a Grouped 3 Skyscrapers. The elimination lands on any cell that shares a house with both roof endpoints. These patterns are rarer than the ungrouped version but appear in harder puzzles where a digit's candidates cluster inside blocks rather than lining up neatly in rows and columns.
The logic
The reasoning is identical to regular 3 Skyscrapers — the grouped link behaves the same way as a single-cell link. Each strong link is a house where the digit has exactly two candidate positions (or two candidate groups, for the grouped link), so one of them must be the digit. In the chain, one candidate from each neighbouring pair sits on a shared line — the bridge. Because the two bridge cells see each other, at most one can be the digit. If the first bridge is the digit, the second link's digit falls on its roof cell and the chain stops. If not, the first link's digit falls on its other cell, which is the next bridge — and the same reasoning carries forward. Every case forces at least one of the two roof cells to contain the digit, so any cell seeing both roof cells can't also hold it. The grouped link doesn't change the logic: a group of cells that can't all hold the digit acts exactly like a single cell that can't hold it.