Rules & objective
Place each height 1–N (N is the grid width) once in every row and column. An edge clue counts buildings visible from that side; taller buildings hide shorter ones behind them.
Controls
Arrows select · Numbers enter · Backspace erases · U undoes
Worked example
Looking along heights 1, 3, 2 reveals only 1 and 3, giving a clue of two. The final 2 is hidden by the taller 3.