Skyscrapers

Hard Skyscrapers jumps to a full 7×7 grid — 49 cells and seven heights per line — with no given cells and several clues hidden. The larger grid alone makes you work a bit extra: lines are longer, so each visibility clue interacts with more cells.

Focus on lines where both the left/top and right/bottom clues are visible; those give you the most to work with. Partial-placement elimination helps too: if putting height 7 in a particular cell would make a nearby clue impossible to satisfy, then 7 cannot go there. Enumerate what each clue permits for a line and intersect it with the Latin-square constraints before committing.

Mid-range clues (3 and 4) leave many arrangements and are the hardest to use; high clues (6 or 7) and low clues (1) are far more constraining, so start there. Every board is uniquely solvable without guessing. If you stall, rescan for a cell that elimination has already reduced to a single candidate.