Given an m x n matrix of integers matrix, return a list of all elements within the matrix in spiral order.

Example 1:

Input: matrix = [[1,2],[3,4]]

Output: [1,2,4,3]

Example 2:

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

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

Example 3:

Input: matrix = [[1,2,3,4],[5,6,7,8],[9,10,11,12]]

Output: [1,2,3,4,8,12,11,10,9,5,6,7]

Constraints:

• 1 <= matrix.length, matrix[i].length <= 10
• -100 <= matrix[i][j] <= 100