Spiral Matrix

You get a grid matrix of integers, with m rows and n columns.

Return a List of its values in spiral order.

matrix is an array of rows. Each row is an array of integers. Row 0 is the top row. Column 0 is the leftmost column.

The spiral starts at the top-left value and goes clockwise around the edge. It goes right along the top row, then down the right column. Then it goes left along the bottom row and up the left column.

Next, it does the same with the smaller grid inside, and so on. It takes each value exactly once.

Example 1:

Input: matrix = [
  [5, 1, 8],
  [0, 3, 2],
  [9, 7, 4]
]
Output: [5, 1, 8, 2, 4, 7, 9, 0, 3]
Explanation: The spiral first goes around the edge:
5, 1 and 8 across the top,
2 and 4 down the right side,
7 and 9 back along the bottom,
0 up the left side.
3 is left in the middle.

Example 2:

Input: matrix = [
  [3, -1, 7],
  [6, 0, 2],
  [1, 5, 9],
  [8, 8, 4]
]
Output: [3, -1, 7, 2, 9, 4, 8, 8, 1, 6, 0, 5]
Explanation: The spiral first goes around the edge:
3, -1 and 7 across the top,
2, 9 and 4 down the right side,
8 and 8 back along the bottom,
1 and 6 up the left side.
Inside, one column is left.
It gives 0, then the 5 below it.

Example 3:

Input: matrix = [
  [-4, 0, 4]
]
Output: [-4, 0, 4]
Explanation: There is only one row.
The spiral goes right along it and stops.
No value is taken twice.

Constraints:

• m and n are each from 1 to 500.
• Each value is an integer from -1000 to 1000.
• Negative values and repeats are allowed.