Spiral Traversal

Given an m x n matrix, return all of its elements in spiral order: starting at the top-left corner, walk right across the top row, down the right column, left across the bottom row, and up the left column, then repeat on the next inner "ring" until every element has been visited.

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

• 1 <= m, n <= 10
• -100 <= matrix[i][j] <= 100
• The matrix is not necessarily square.