Spiral Matrix II @leetcode

Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.

For example,
Given n = 3,

You should return the following matrix:
[
 [ 1, 2, 3 ],
 [ 8, 9, 4 ],
 [ 7, 6, 5 ]
]
» Solve this problem

This problem has nothing very special, only if you can figure out the regularity of how index changes of the matrix.

I set many counters to calculate.