2002 AIME II Problem 1

Given that x and y are both integers between 100 and 999, inclusive; y is the number formed by reversing the digits of x; and z=|x-y|. How many distinct values of z are possible?

Leading zeroes must be inputted, so if your answer is 34, then input 034

Full credit goes to MAA for authoring these problems. These problems were taken on the AOPS website.