Spiral Matrix leetcode

Given a matrix of m x n elements (m rows, n columns), 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].

就是一层一层的处理矩阵, 实现中要注意两个细节，一个是因为题目中没有说明矩阵是不是方阵，因此要先判断一下行数和列数来确定螺旋的层数。另一个是走一次是走两行两列, 但是如果遇(行和列中间最小的是)单数的, 还要再判定一下然后继续走完. 

时间复杂度O(m*n)空间O(1)

public class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> res = new ArrayList<Integer>();
        if (matrix == null || matrix.length == 0 || matrix[0].length == 0) {
            return res;
        }
        int row = matrix.length;
        int col = matrix[0].length;
        int min = Math.min(row, col);
        int mid = min / 2;
        for (int i = 0; i < mid; i++) {
            for (int j = i; j < col - i - 1; j++) {
                res.add(matrix[i][j]);
            }
            for (int j = i; j < row - i - 1; j ++) {
                res.add(matrix[j][col - i - 1]);
            }
            for (int j = col - i - 1; j > i; j--) {
                res.add(matrix[row - i - 1][j]);
            }
            for (int j = row - i -1; j > i; j--) {
                res.add(matrix[j][i]);
            }
        }
        if (min % 2 == 1) {
            if (row < col) {
                for (int j = mid; j < col - mid; j++) {
                    res.add(matrix[mid][j]);
                }
            } else {
                for (int j = mid; j < row - mid; j++) {
                    res.add(matrix[j][mid]);
                }
            }
        }
        return res;
    }
}