题目：
Given a matrix of m x n elements (m rows, ncolumns), return all elements of the matrix in spiral order.
For example,
Given the following matrix:
[ [ 1, 2, 3 ], [ 4, 5, 6 ], [ 7, 8, 9 ] ]
You should return [1,2,3,6,9,8,7,4,5].
链接：
题解：
测试：
原文：http://www.cnblogs.com/yrbbest/p/4436371.html