如何高效统计文本文件中各文件夹的直接子项数量？

我有一个存储文件夹路径的文本文件，内容示例如下：

Folder1
Folder1/SubFolder1
Folder1/SubFolder1/SubSubFolder1
Folder1/SubFolder1/SubSubFolder2
Folder1/SubFolder1/SubSubFolder3
Folder1/SubFolder1/SubSubFolder4
Folder1/SubFolder2
Folder1/SubFolder2/SubSubFolder1
Folder1/SubFolder2/SubSubFolder2
Folder1/SubFolder2/SubSubFolder3
Folder1/SubFolder2/SubSubFolder4
Folder1/SubFolder2/SubSubFolder5
Folder1/SubFolder2/SubSubFolder6
Folder1/SubFolder2/SubSubFolder6/SubSubSubFolder1
Folder1/SubFolder3
Folder2
Folder2/SubFolder1
Folder2/SubFolder1/SubSubFolder1
Folder2/SubFolder1/SubSubFolder2
Folder2/SubFolder1/SubSubFolder3
Folder2/SubFolder1/SubSubFolder4
Folder2/SubFolder2
Folder2/SubFolder2/SubSubFolder1
Folder2/SubFolder2/SubSubFolder2
Folder2/SubFolder2/SubSubFolder3
Folder2/SubFolder2/SubSubFolder4
Folder2/SubFolder2/SubSubFolder5
Folder2/SubFolder2/SubSubFolder6
Folder2/SubFolder2/SubSubFolder7
Folder2/SubFolder2/SubSubFolder6/SubSubFolder1
Folder2/SubFolder3
Folder2/SubFolder4

需要生成一个<string, int>类型的字典，记录每个文件夹名称及其直接子项（仅顶层）的数量，示例输出如下：

Folder1, 3                  // SubFolder1, SubFolder2, SubFolder3
Folder1/SubFolder1,4            // SubSubFolder1, SubSubFolder2, SubSubFolder3, SubSubFolder4
Folder1/SubFolder2,6       //SubSubFolder1, SubSubFolder2, SubSubFolder3, SubSubFolder4, SubSubFolder5, SubSubFolder6
Folder1/SubFolder2/SubSubFolder6,1         //SubSubSubFolder1
Folder1/SubFolder3,0
Folder2,4                // SubFolder1, SubFolder2, SubFolder3, SubFolder4
Folder2/SubFolder1,4        // SubSubFolder1, SubSubFolder2, SubSubFolder3, SubSubFolder4
Folder2/SubFolder2,7       // SubSubFolder1, SubSubFolder2, SubSubFolder3, SubSubFolder4, SubSubFolder5, SubSubFolder6, SubSubFolder7
Folder2/SubFolder2/SubSubFolder6,1             //SubSubSubFolder1
Folder2/SubFolder3,0  
Folder2/SubFolder4,0 

目前我能通过遍历所有行实现，但方法复杂繁琐，现有代码片段如下：

var allLines = File.ReadAllLines(filePath);
foreach (var line in allLines)
{
    var subFolderCount = 0;
    var subFolderPath = Path.Combine(folderPath, line);
    //...
}

请问是否有更简便高效的实现方式？

可以利用LINQ分组统计+字典初始化的方式简化逻辑，核心思路是先统计每个父路径的直接子项数量，再将所有原始路径纳入字典，无直接子项的路径计数设为0。具体代码如下：

var allLines = File.ReadAllLines(filePath);

// 第一步：统计每个父路径对应的直接子项数量
var parentChildCounts = allLines
    .Where(line => !string.IsNullOrWhiteSpace(line) && line.Contains('/'))
    .Select(line => line.Substring(0, line.LastIndexOf('/'))) // 提取当前路径的父路径
    .GroupBy(parentPath => parentPath)
    .ToDictionary(group => group.Key, group => group.Count());

// 第二步：生成包含所有路径的最终字典，无直接子项的路径计数为0
var folderChildCounts = allLines
    .Distinct() // 处理文本中可能存在的重复路径
    .ToDictionary(
        folderPath => folderPath,
        folderPath => parentChildCounts.TryGetValue(folderPath, out var count) ? count : 0
    );

// 可选：打印结果验证
foreach (var kvp in folderChildCounts)
{
    Console.WriteLine($"{kvp.Key}, {kvp.Value}");
}

逻辑说明 #

1. 第一部分通过LINQ筛选出有父路径的项，提取父路径后分组统计，快速得到每个父路径对应的直接子项数量
2. 第二部分将所有原始路径转为字典，对于每个路径，从统计结果中获取子项数量，不存在则设为0
3. 该方式避免了嵌套遍历，时间复杂度为O(n)，比逐行判断的逻辑更简洁高效

内容的提问来源于stack exchange，提问作者Pankaj