Problem: Spiral Matrix

Given an $m\times n$ matrix, return an array containing the matrix elements in spiral order, starting from the top-left cell.

Constraints:

• $1\leq$ matrix.length $\leq 10$
• $1\leq$ matrix[i].length $\leq 10$
• $-100\leq$ matrix[i][j] $\leq 100$