c#求幂集结果只记录了LIST长度，没有记录具体元素

Question

比如A={1,2,3},那么A的幂集为P（A）={{1,2,3},{1,2},{1,3},{1},{2,3},{2},{3},{空}}

static void Main(string[] args)
{
    ArrayList A = new ArrayList();
    A.Add("1");
    A.Add("2");
    A.Add("3");
    A.Add("4");
    ArrayList B = new ArrayList();
    List<ArrayList> C = new List<ArrayList>(); // 结果集
    Program p = new Program();
    p.GetPowerSet(0, A, B, ref C);
    Console.WriteLine(C.Count);
    Console.ReadLine();
}

void GetPowerSet(int i, ArrayList A, ArrayList B, ref List<ArrayList> C)
{
    if (i == A.Count)
    {
        C.Add(B);
    }
    else
    {
        string x = GetElem(A, i);
        int k = GetLength(B);
        B.Insert(k, x);
        GetPowerSet(i + 1, A, B, ref C);
        B.RemoveAt(k);
        GetPowerSet(i + 1, A, B, ref C);
    }
}

string GetElem(ArrayList A, int i)
{
    return A[i].ToString();
}

int GetLength(ArrayList A)
{
    int i = 0;
    foreach (string a in A)
    {
        if (a != "0")
        {
            i++;
        }
    }
    return i;
}

最后想要的结果不对，显示成了
我该怎么解决呢？

Answer 1

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

public class Test
{
    static List<List<int>> GetPowerSet(List<int> list)
    {
        return Enumerable.Range(0, 1 << list.Count())
        .Select(x => list.Select((y, i) => new { y, i }).Where(y => (x & (1 << y.i)) == (1 << y.i)).Select(y => y.y).ToList())
        .ToList();
    }
    public static void Main()
    {
        // your code goes here
        List<int> list = new List<int>() {1,2,3};
        foreach (var item in GetPowerSet(list))
        {
            Console.WriteLine(string.Join(",", item));
        }
    }
}