Index Skyscrapers (452)

Insert number from 1 to N where N is the size of the grid into each cell so that no digit is repeated within a row or a column. Each number in the grid represents the height of a skyscraper. The clues inside the grid indicate the number of directions the skyscraper is visible from, when looking from the outside of the grid from the corresponding direction. Higher skyscrapers block the view of smaller ones.

Reference: WPC 2016 (65)