Skyscrapers consists of a square grid. The goal is to fill in each cell with numbers from 1 to N, where N is the size of the puzzle's side. No number may appear twice in any row or column. The numbers along the edge of the puzzle indicate the number of buildings which you would see from that direction if there was a series of skyscrapers with heights equal the entries in that row or column.
The grid may contain empty cells ("parks"). Each row and column has exactly one of each digit and one park.
In Sum Skyscrapers the number outside the grid indicates the sum of heights of visible buildings.
Cross+A can solve puzzles from 3 x 3 to 9 x 9.