题目描述

输入一个矩阵，按照从外向里以顺时针的顺序依次打印出每一个数字。

样例

输入：
[
  [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]

算法1

$O(n^2)$

时间复杂度

JAVA 代码

class Solution {
    public int[] printMatrix(int[][] matrix) {
        if (matrix.length == 0 || matrix[0].length == 0) {
            return new int[0];
        }

        int m = matrix.length;
        int n = matrix[0].length;

        int[] res = new int[m * n];

        int[] dx = {0, 1, 0, -1}, dy = {1, 0, -1, 0};
        int x = 0, y = 0, d = 0;
        int[][] mark = new int[m][n];

        for (int i = 0; i < m*n; i++) {
            res[i] = matrix[x][y];
            mark[x][y] = 1;

            int a = x + dx[d];
            int b = y + dy[d];
            if (a < 0 || a >= m || b < 0 || (b) >= n || mark[a][b] == 1){
                d = (d + 1) % 4;
                a = x + dx[d];
                b = y + dy[d];
            } 
            x = a;
            y = b;
        }
        return res;

    }
}