combination sum

Solution.cs

using System;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.Linq;

public class Solution
{

    public class ListBak
    {
        public List<int> List { get; set; }

        public ListBak(List<int> List)
        {
            this.List = List;
        }

        public override int GetHashCode()
        {
            var hash = 0;

            foreach (var item in List)
            {
                hash += HashCode.Combine(item);
            }

            return hash;
        }

        public override bool Equals(object obj)
        {
            return GetHashCode() == obj.GetHashCode();
        }
    }

    public class ObjectEqualityComparer : IEqualityComparer<ListBak>
    {
        public bool Equals([AllowNull] ListBak x, [AllowNull] ListBak y)
        {
            return x.Equals(y);
        }

        public int GetHashCode([DisallowNull] ListBak obj)
        {
            return obj.GetHashCode();
        }
    }

    private HashSet<ListBak> sumList = new HashSet<ListBak>(new ObjectEqualityComparer());
    private int target;
    private int[] candidates;

    public IList<IList<int>> CombinationSum(int[] candidates, int target)
    {
        Array.Sort(candidates);
        this.candidates = candidates;
        this.target = target;

        this.SearchCandidates(0, new Stack<int>());

        return sumList.Select(e=> e.List).Cast<IList<int>>().ToList();
    }


    private void SearchCandidates(int sum, Stack<int> runningSum)
    {
        if (sum == target)
        {
            var lst = new ListBak(new List<int>(runningSum));
            lst.List.Sort();
            sumList.Add(lst);
            return;
        }
        else if(sum > target)
        {
            return;
        }
        else
        {
            for (int i = 0; i < candidates.Length; i++)
            {
                runningSum.Push(candidates[i]);
                sum += candidates[i];
                this.SearchCandidates(sum, runningSum);
                sum -= candidates[i];
                runningSum.Pop();
            }
        }
    }


}