Number is say XY then u can write it as 10X+Y.
Now you are doing 10X+Y - (10Y+X) which is 9(X-Y) where X and Y lie between 0 and 9 . when X >Y you get multiples of 9 in increasing order and when X <Y you get them in decreasing order. when X==Y , you get 0. --------------------------------- Get a bigger mailbox -- choose a size that fits your needs.
