[LeetCode] Spiral Matrix

最新推荐文章于 2025-11-30 19:25:58 发布

转载最新推荐文章于 2025-11-30 19:25:58 发布 · 84 阅读

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原文链接：https://segmentfault.com/a/1190000009683626

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#数据结构与算法

本文介绍了一种螺旋矩阵遍历算法，该算法可以按螺旋顺序返回矩阵中的所有元素。适用于不同大小和形状的矩阵，包括特殊情况如单行或单列矩阵。通过四个基本步骤：向右、向下、向左、向上进行遍历，并避免重复访问。

Spiral Matrix

Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.

Time Complexity
O(mn)

思路

We should think about these test cases :
if matrix == null, matrix.length == 0, matrix[0] == null, matrix[0].length == 0
if matrix just has one row
1 2 3

if matrix just has one column
1
2
3
if matrix is even
1 2 3 4
5 6 7 8
9 10 11 12
13 14 15 16

we're going to print it in this order
1 2 3 4
8 12 16
15 14 13
9 5
6 7
11
10

if matrix is odd
1 2 3 4 5 6
7 8 9 10 11 12
13 14 15 16 17 18

print it in this order
1 2 3 4 5 6
12 18
17 16 15 14 13
7

if(rowStart > rowEnd || colStart > colEnd) break; it means it just have one row or one col left, so when it finish go right and go down. It should not do go left and go down anymore.

代码

public List<Integer> spiralOrder(int[][] matrix) {
    List<Integer> res = new ArrayList<Integer>();
    //corner case
    if(matrix == null || matrix.length == 0 || matrix[0] == null || matrix[0].length == 0) return res;
    int rows = matrix.length, cols = matrix[0].length;
    int rowStart = 0, colStart = 0, rowEnd = rows - 1, colEnd = cols - 1;
    
    while(rowStart <= rowEnd && colStart <= colEnd){
        //go right
        for(int i = colStart; i <= colEnd; i++){
            res.add(matrix[rowStart][i]);
        }
        rowStart++;
        //go down
        for(int i = rowStart; i <= rowEnd; i++){
            res.add(matrix[i][colEnd]);
        }
        colEnd--;
        
        if(rowStart > rowEnd || colStart > colEnd) break;
        
        //go left
        for(int i = colEnd; i >= colStart; i--){
            res.add(matrix[rowEnd][i]);
        }
        rowEnd--;
        
        //go up
        for(int i = rowEnd; i >= rowStart; i--){
            res.add(matrix[i][colStart]);
        }
        colStart++;
    }
    return res;
}