Good hashcode function for 2D coordinates

Question

I would like to use a HashMap to map (x, y) coordinates to values. What is a good hashCode() function definition? In this case, I am only storing integer coordinates of the form (x, y) where y - x = 0, 1, ..., M - 1 for some parameter M.

Answer 1

To get unique Value from two numbers, you can use bijective algorithm described in here < x; y >= x + (y + ( (( x +1 ) /2) * (( x +1 ) /2) ) )

This will give you unquie value , which can be used for hashcode

public int hashCode()
{
      int tmp = ( y +  ((x+1)/2));
               return x +  ( tmp * tmp);
}