Spiral Matrix

Given an m × n matrix, return all elements of the matrix in spiral order.

Example 1:

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

Example 2:

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:

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