How do you rotate a two dimensional array?

Question

Inspired by Raymond Chen\'s post, say you have a 4x4 two dimensional array, write a function that rotates it 90 degrees. Raymond links to a solution in pseudo code, but I\'d

Answer 1

#transpose is a standard method of Ruby's Array class, thus:

% irb
irb(main):001:0> m = [[1, 2, 3, 4], [5, 6, 7, 8], [9, 0, 1, 2], [3, 4, 5, 6]]
=> [[1, 2, 3, 4], [5, 6, 7, 8], [9, 0, 1, 2], [3, 4, 5, 6]] 
irb(main):002:0> m.reverse.transpose
=> [[3, 9, 5, 1], [4, 0, 6, 2], [5, 1, 7, 3], [6, 2, 8, 4]]

The implementation is an n^2 transposition function written in C. You can see it here: http://www.ruby-doc.org/core-1.9.3/Array.html#method-i-transpose by choosing "click to toggle source" beside "transpose".

I recall better than O(n^2) solutions, but only for specially constructed matrices (such as sparse matrices)