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]

 

题意：螺旋矩阵，按螺旋的方式打印

有的题也叫蛇形矩阵，题本身不难，就是遍历，和越界问题。

主要考验的是耐心和细心

class Solution {    public List
       
         spiralOrder(int[][] matrix) {        int n = matrix.length;        if (n == 0)            return new ArrayList<>();        int m = matrix[0].length;        if (m == 0)            return new ArrayList<>();        List
        
          res = new ArrayList<>(m * n);        int k = 0;        int i = 0;        int j = 0;        boolean left = true;        boolean down = false;        boolean up = false;        boolean right = false;        int sum = m * n;        int upn = -1;        int upm = -1;        while (k