Hidden Quad
Hard
Used by Smart Hint
Four heights only fit in the same four cells of a row or column — strip those cells down to just those four.
- Cells that establish the pattern
- Where the conclusion lands
- Height ruled out
How it works
- A 6x6 board, so heights run 1 to 6. Track the top four — 3, 4, 5 and 6 — across this row.
- None of them fits in the first two cells, which are down to {1, 2}.
- That confines four heights to four cells, so those cells hold exactly those four between them.
- Strike the leftover 1s and 2s. As with every hidden subset, no cell is settled yet — the row is just four eliminations tidier.
- This shape needs a board bigger than plain Skyscrapers' 5x5 to say anything at all, which is why it's rare until you're deep into Skyscrapers+.