DouKaku?

using System;
using System.Linq;
using System.Collections.Generic;

static class Program {
    static string RemoveAfter(this string s, char ch) {
        int index = s.IndexOf(ch);
        return (0 <= index && index < s.Length - 1) ? s.Remove(index + 1) : s;
    }
    static void ls(IEnumerable<string> pathList, string path) {
        if (!path.EndsWith("/")) path += '/';

        var x = from y in pathList where y.StartsWith(path)
                select '"' + y.Substring(path.Length).RemoveAfter('/') + '"';

        Console.WriteLine("[{0}]", string.Join(", ", x.Distinct().ToArray()));
    }
    static void Main(string[] args) {
        string[] pathList = { "aaa/bbb", "aaa/ccc", "aaa/ddd/eee", "bbb/ddd/eee" };

        ls(pathList, "aaa/");
        ls(pathList, "aaa/ddd/");
    }
}