From: Markus <markus@...>
Date: 2004-09-23T08:05:44+09:00
Subject: Re: Newbie: Case statement

> So my underlying question is:- what's the fastest Ruby for checking 
> which of the 8 possible adjacent cells on a board (2D array) are 
> still "on the board"

given x,y:

x_range = (x=min_x ? x : x-1)..(x=max_x ? x : x+1)
y_range = (y=min_y ? y : y-1)..(y=max_y ? y : y+1)
x_range.collect { |x0|
    y_range.collect { |y0| [x0,y0] unless x0 == x and y0 == y}
    }.compact

might do what you want.  Depends on what you mean by fast.

-- Markus

P.S. In use, this might be something more like:

class A_chess_board
    attr_reader :min_x,:min_y,:max_x,:max_y

    def for_each_neighbor_of(x,y)
        x_range = (x=min_x ? x : x-1)..(x=max_x ? x : x+1)
        y_range = (y=min_y ? y : y-1)..(y=max_y ? y : y+1)
        x_range.collect { |x0|
            y_range.collect { |y0| 
                yield(x0,y0) unless x0 == x and y0 == y}
                }
            }
        }
    end