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:
    vector<int> spiralOrder(vector<vector<int>>& matrix) {
        	vector<int> res;
	int h = matrix.size();
	if (h == 0)return res;
	int w = matrix[0].size();
	if (w == 0)return res;
	vector<vector<bool> > visit(h, vector<bool>(w, false));
	bool flag = true;
	for (int i = 0, j = 0; flag;) {
		flag = false;
		while (j < w && !visit[i][j]) {
			res.push_back(matrix[i][j]);
			visit[i][j] = true;
			j++;
			flag = true;
		}
		j--; i++;
		while (i < h && !visit[i][j]) {
			res.push_back(matrix[i][j]);
			visit[i][j] = true;
			i++;
			flag = true;
		}
		i--; j--;
		while (j >= 0 && !visit[i][j]) {
			res.push_back(matrix[i][j]);
			visit[i][j] = true;
			j--;
			flag = true;
		}
		j++; i--;
		while (i >= 0 && !visit[i][j]) {
			res.push_back(matrix[i][j]);
			visit[i][j] = true;
			i--;
			flag = true;
		}
		i++; j++;
	}

	return res;
    }
};

多做题，多思考