剑指 Offer 29. 顺时针打印矩阵（简单）

Leetcode链接：剑指 Offer 29. 顺时针打印矩阵

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。

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]

限制：

0 <= matrix.length <= 100

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

源码

class Solution {
    public int[] spiralOrder(int[][] matrix) {
        int m = matrix.length;
        if(m == 0) return new int[0]; 
        int n = matrix[0].length;
        if(n == 0) return new int[0];

        int up = 0;
        int down = m - 1;
        int left = 0;
        int right = n - 1;

        int index = 0;
        int[] res = new int[m * n];

        while(left <= right && up <= down){
            
            for(int col = left; col <= right; col ++){
                res[index ++] = matrix[up][col];
            }
            up ++;

            for(int row = up; row <= down; row++){
                res[index ++] = matrix[row][right];
            }
            right --;

            if(left > right || up > down) break;

            for(int col = right; col >= left; col --){
                res[index ++] = matrix[down][col];
            }
            down --;

            for(int row = down; row >= up; row --){
                res[index ++] = matrix[row][left];
            }
            left ++;
        }

        return res;
    }
}