Fill every cell with a number 1-7 so each row and column contains every number exactly once - like Sudoku, but
with no boxes. The numbers around the edge tell you how many "buildings" (their heights) are visible looking
into that row or column from that side - a taller building blocks any shorter ones behind it.
- Tap a cell, then tap a number on the keypad below to fill it in.
- Notes toggles pencil-mark mode - tap numbers to jot down candidates in a cell instead of
filling it in for real.
- An edge clue turns green once its whole row/column is filled in correctly, or
red if it's full but wrong.
- Wrong entries are marked as mistakes and cost points every time; the timer also counts down your score.
- Undo / Redo step backward or forward. Erase clears the selected cell.
Hint reveals one correct cell (limited per puzzle, costs points). Pause
hides the board and stops the timer.
