题目：

Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.

Example 1:

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

Example 2:

Input:
[
  [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]

 

代码：

class Solution {
public:
    void backOrder(vector<vector<int>>& matrix, vector<int>& backorder, int starti, int startj, int m, int n)
	{
		if (starti >= m || startj >= n)
			return;
		for (int j = startj; j < n; j++)
			backorder.push_back(matrix[starti][j]);
		for (int i = starti + 1; i < m && n >= 1; i++)
			backorder.push_back(matrix[i][n - 1]);
		for (int j = n - 2; j >= startj && m - starti > 1; j--)
			backorder.push_back(matrix[m - 1][j]);
		for (int i = m - 2; i > starti && n - startj > 1; i--)
			backorder.push_back(matrix[i][startj]);
		return backOrder(matrix, backorder, starti + 1, startj + 1, m - 1, n - 1);
	}
	vector<int> spiralOrder(vector<vector<int>>& matrix) {
		vector<int> res;
		int m = matrix.size();
		if (m < 1)
			return res;
		int n = matrix[0].size();
		backOrder(matrix, res, 0, 0, m, n);
		return res;
	}
};