[LeetCode]Spiral Matrix

从里到外一层一层剥洋葱即可，注意最后只剩一行或者一列的时候不要重复访问。时间复杂度O(n)，空间复杂度O(1)，代码如下：

	class Solution {
	public:
	vector<int> spiralOrder(vector<vector<int>>& matrix) {
	int m = matrix.size(), n = m? matrix[0].size(): 0, layers = (min(m, n) + 1) / 2;
	vector<int> res;
	for(int k = 0; k < layers; ++k)
	{
	for(int j = k; j < n - k; ++j)
	res.push_back(matrix[k][j]);
	for(int i = k + 1; i < m - k - 1; ++i)
	res.push_back(matrix[i][n - k - 1]);
	for(int j = n - k - 1; j >= k; --j)
	if(m - k - 1 != k)
	res.push_back(matrix[m - k - 1][j]);
	for(int i = m - k - 2; i >= k + 1; --i)
	if(n - k - 1 != k)
	res.push_back(matrix[i][k]);
	}
	return res;
	}
	};

view raw Spiral Matrix.cpp hosted with ❤ by GitHub