HOW to build a sudoku -?? ( not to solve it ) any idea ?

I've been wondering about that, too. I think maybe the easiest route would be to design whole boards, then remove a certain number of blocks depending on whether it's easy, medium or hard. It's not a foolproof way to set the difficulty because it also depends on the placement of the numbers remaining, but it seems much easier than trying to get it to work out how many logical steps are needed to solve each puzzle. You could use a randomiser to choose which blocks to remove, as well as to shuffle the numbers around to generate a new complete board. I don't know how to program, but there should be some sort of logical commands to govern the arrangement of the numbers. Probably the easiest would be 3 commands: (Each row contains number 1. Each column contains number 1. Each square contains number 1) and then repeat them for each number.