leetcode每日一題6.5面試題29. 順時針打印矩陣

輸入一個矩陣，按照從外向裏以順時針的順序依次打印出每一個數字。

示例 1：

輸入：matrix = [[1,2,3],[4,5,6],[7,8,9]]
輸出：[1,2,3,6,9,8,7,4,5]
示例 2：

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

限制：

0 <= matrix.length <= 100
0 <= matrix[i].length <= 100

思路：看代碼

class Solution {
    public int[] spiralOrder(int[][] matrix) {
        if (matrix.length == 0) {
            return new int[0];
        }
        int[] res = new int[matrix.length * matrix[0].length];
        int up = 0;
        int down = matrix.length-1;
        int l = 0;
        int r = matrix[0].length-1;
        int index = 0;
        while (true) {
            for (int i = l; i <= r; i++) {//向右
                res[index++] = matrix[up][i];
            }
            if (++up > down) {//up層走完了，所以up+1(也有爲接下來的for做準備)，加入up大於down了，就說明遍歷完成了
                break;
            }
            for (int i = up; i <= down; i++) {//往下走
                res[index++] = matrix[i][r];
            }
            if (--r < l) {
                break;
            }
            for (int i = r; i >= l; i--) {//往左走
                res[index++] = matrix[down][i];
            }
            if (--down < up) {
                break;
            }
            for (int i = down; i >= up; i--) {//往上走
                res[index++] = matrix[i][l];
            }
            if (++l > r) {
                break;
            }
        }
        return res;
    }
}