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

**Example 1:**

![](https://assets.leetcode.com/uploads/2020/11/13/spiraln.jpg)

    Input: n = 3
    Output: [[1,2,3],[8,9,4],[7,6,5]]
    

**Example 2:**

    Input: n = 1
    Output: [[1]]
    

**Constraints:**

*   `1 <= n <= 20`