leetcode原地址：https://leetcode.cn/problems/spiral-matrix/description

描述

给你一个 m 行 n 列的矩阵 matrix ，请按照 顺时针螺旋顺序 ，返回矩阵中的所有元素。

示例 1：

输入：matrix = [[1,2,3],[4,5,6],[7,8,9]]
输出：[1,2,3,6,9,8,7,4,5]

示例 2：

输入：matrix = [[1,2,3,4],[5,6,7,8],[9,10,11,12]]
输出：[1,2,3,4,8,12,11,10,9,5,6,7]

提示：

m == matrix.length
n == matrix[i].length
1 <= m, n <= 10
-100 <= matrix[i][j] <= 100

题解

    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> res = new ArrayList<>();
        if (matrix == null || matrix.length == 0 || matrix[0].length == 0) {
            return res;
        }
        int top  = 0;
        int left  = 0;
        int right  = matrix[0].length-1;
        int bottom  = matrix.length-1;
        int cur = 0;
        while (right>left && bottom >top){
            //从左往右
            for(int i =left;i<right;i++){
                res.add(matrix[top][i]);
            }
            //从上到下
            for(int i =top;i<bottom;i++){
                res.add(matrix[i][right]);
            }
            //从右往左
            for(int i =right;i>left;i--){
                res.add(matrix[bottom][i]);
            }
            //从下到上
            for(int i =bottom;i>top;i--){
                res.add(matrix[i][left]);
            }
            left++;
            bottom--;
            top++;
            right--;
        }
        if (top == bottom) {
            for (int i = left; i <= right; i++) {
                res.add(matrix[top][i]);
            }
        } else if (left == right) {
            for (int i = top; i <= bottom; i++) {
                res.add(matrix[i][left]);
            }
        }
        return res;
    }