LeetCode: 54. Spiral Matrix（Medium）

1. 原题链接

https://leetcode.com/problems/spiral-matrix/description/

2. 题目要求

给定一个二维整型数组，返回其螺旋顺序列表，例如：

最后返回结果为 [1,2,3,6,9,8,7,4,5]

3. 解题思路

按照螺旋的顺序进行遍历，每一次遍历螺旋顺序里的一个圈，如下图每一种颜色代表一次遍历得到的结果

4. 代码实现

import java.util.ArrayList;
import java.util.List;

public class SpiralMatrix54 {
    public static void main(String[] args) {
        int[][] matrix = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}, {0, 0, 0}};
        System.out.println(spiralOrder(matrix).toString());
    }

    public static List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> res = new ArrayList<Integer>();
        if (matrix.length == 0) return res;
        int rowBegain = 0, rowEnd = matrix.length - 1;  // 行数
        int colBegain = 0, colEnd = matrix[0].length - 1;  // 列数
        while (rowBegain <= rowEnd && colBegain <= colEnd) {  // 一次遍历一个螺旋顺序的圈
            for (int i = colBegain; i <= colEnd; i++) {
                res.add(matrix[rowBegain][i]);
            }
            rowBegain++;

            for (int i = rowBegain; i <= rowEnd; i++) {
                res.add(matrix[i][colEnd]);
            }
            colEnd--;

            if (rowBegain <= rowEnd) {
                for (int i = colEnd; i >= colBegain; i--)
                    res.add(matrix[rowEnd][i]);
            }
            rowEnd--;

            if (colBegain <= colEnd) {
                for (int i = rowEnd; i >= rowBegain; i--)
                    res.add(matrix[i][colBegain]);
            }
            colBegain++;
        }

        return res;

    }
}