How to play
Fill an N×N grid with buildings of height 1 to N. Every row and every column holds each height exactly once.
A number outside the grid tells you how many buildings are visible when you look along that row or column from that side. A taller building hides every lower one behind it.
Some sheets also print a few heights inside the grid. Each puzzle has exactly one solution; tap a cell and pick a height from the pad, or switch on notes to pencil in candidates.
Strategy and tips
- A clue of 1 means the tallest building stands right next to it.
- A clue equal to N means the line rises 1, 2, 3 … N in order from that side, so the whole line is fixed at once.
- Big clues keep tall buildings away. With a clue of c, the cell at distance d from it (counting the nearest cell as 1) can hold at most N − c + d. So a clue of 3 in a 5×5 grid caps the first cell at 3 and the second at 4.
- Read opposite clues together. A line seen as 1 from one end has its tallest building at that end, so from the far end the tallest building comes last and the far clue counts the buildings that rise before it.
- Once the tallest buildings are placed, treat the next height as the new tallest among the remaining cells and repeat the same reasoning.
- Use notes for the tall heights. Pencil in where N and N − 1 can still go in each row and column; when a height has only one possible cell left in a line, place it, just as you would a hidden single in sudoku.
Questions
- What changes between levels?
- The grid grows from 4×4 to 5×5, 6×6 and 7×7, and fewer edge clues are kept. When the edge clues alone would not be enough, a few heights are printed inside the grid.
- Can two buildings of the same height hide each other?
- That never happens: heights in a line are always different, so every building is either taller than all the ones before it (visible) or hidden.
- Can I write notes?
- Yes. Toggle the pencil on the pad, or press N on a keyboard, to note possible heights in a cell.
- How do I play with a keyboard?
- Arrow keys move between cells, the number keys enter a height, Shift plus a number writes a note, N toggles notes and Backspace or 0 clears. H asks for a hint, and Ctrl+Z and Ctrl+Y undo and redo.
- What does the hint do?
- It finds a cell whose height is forced by the clues in your current position and shows it to you. If you have already placed a wrong height, the hint points at that cell first.