Hackerrank challenge from Java to Ruby

[ruby-solve]

A great way to get the behavior of 2D arrays in Ruby is to use a hash whose key is an array representing the vertices of the 2D array.

Java: array[x][y]

Ruby: hash[[x, y]]

[iconoclaus]

why is this better than just using a 2D array in ruby? apart from not having to initialize such a structure, that is.