Just enter the numbers line by line separated by spaces or commas and click Solve. You can copy and paste the number even if they are not separated to lines correctly. They will be arranged in a square automatically. You can click one of the size buttons to set the number of values in each line.
Hitori Solver Online can solve any rectangular Hitori puzzle (not necessarily square) up to a size of 25x25 in usually less than a second.