Spiral Matrix

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].

java

class Solution {    public List<Integer> spiralOrder(int[][] matrix) {        List<Integer> path = new ArrayList<>();        if (matrix == null || matrix.length == 0 || matrix[0] == null || matrix[0].length == 0) {            return path;        }        int start = 0;        int row = matrix.length;        int column = matrix[0].length;        while (row > 2 * start && column > 2 * start) {            fillPath(matrix, start++, path);        }        return path;    }    private void fillPath(int[][] matrix, int start, List<Integer> path) {        int endX = matrix[0].length - start - 1;        int endY = matrix.length - start - 1;        // 从左到右        for (int i = start; i <= endX; i++) {            path.add(matrix[start][i]);        }        // 从下到上        if (start < endY) {            for (int i = start + 1; i <= endY; i++) {                path.add(matrix[i][endX]);            }        }        // 从右到左        if (start < endX && start < endY) {            for (int i = endX - 1; i >= start; i--) {                path.add(matrix[endY][i]);            }        }        // 从上到下        if (start < endX && start < endY - 1) {            for (int i = endY - 1; i > start; i--) {                path.add(matrix[i][start]);            }        }    }}