Spiral Matrix

Given the size, return a square matrix of numbers in spiral order.

The matrix should be filled with natural numbers, starting from 1 in the top-left corner, increasing in an inward, clockwise spiral order, like these examples:

Examples

Spiral matrix of size 3

1 2 3
8 9 4
7 6 5

Spiral matrix of size 4

 1  2  3 4
12 13 14 5
11 16 15 6
10  9  8 7