Leetcode 题目解析之 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.

    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> rt = new ArrayList<Integer>();
        if (matrix == null || matrix.length == 0) {
            return rt;
        }
        int startx = 0, endx = matrix.length - 1;
        int starty = 0, endy = matrix[0].length - 1;
        while (startx <= endx && starty <= endy) {
            // 上边的行，从左向右
            for (int y = starty; y <= endy; y++) {
                rt.add(matrix[startx][y]);
            }
            // 右边的列，从上到下
            for (int x = startx + 1; x <= endx; x++) {
                rt.add(matrix[x][endy]);
            }
            // 如果行或列遍历完，则退出循环
            if (startx == endx || starty == endy) {
                break;
            }
            // 下边的行，从右向左
            for (int y = endy - 1; y >= starty; y--) {
                rt.add(matrix[endx][y]);
            }
            // 左边的列，从下到上
            for (int x = endx - 1; x >= startx + 1; x--) {
                rt.add(matrix[x][starty]);
            }
            startx++;
            starty++;
            endx--;
            endy--;
        }
        return rt;
    }