The Challenge

The shortest code by character count that takes a single input integer N (N >= 3) and returns an array of indices that when iterated would traverse an NxN matrix according to the JPEG "zigzag" scan pattern. The following is an example traversal over an 8x8 matrix (referenced from here:)

Examples

(The middle matrix is not part of the input or output, just a representation of the NxN matrix the input represents.)

                1 2 3
(Input) 3  -->  4 5 6  -->  1 2 4 7 5 3 6 8 9 (Output)
                7 8 9

                1  2  3  4
(Input) 4  -->  5  6  7  8  -->  1 2 5 9 6 3 4 7 10 13 14 11 8 12 15 16 (Output)
                9 10 11 12
               13 14 15 16

Notes:

• The resulting array's base should be appropriate for your language (e.g., Matlab arrays are 1-based, C++ arrays are 0-based).
• This is related to this question.