Skyscrapers

Rules: Enter a number between 1 and N (where N is the side of the grid) in each cell so that no row or column contains two equal numbers. Each number represents a building of that height. A clue indicates the number of buildings visible when looking down the corresponding row or column from that vantage point, with taller buildings hiding the smaller ones from view.

Example:

sky-0[Solution]

Here is Roland Voigt’s rules page.