CODE

public class Solution {
  List<List<int>> result = new List<List<int>>();
  public List<List<int>> SubsetsWithDup(int[] nums) {
    List<int> subset = new List<int>();
    List<int> empty = new List<int>();
    result.Add(empty);
    List<int> numsList = new List<int>();
    foreach (var n in nums)
      numsList.Add(n);

    findSubset(numsList, 0, subset);
    return result;   
  }

  int currentIndex = 0;
  int lastInd = -1;
  void findSubset(List<int> nums, int index, List<int> subset)
  {
    /* base case */
    if (index > nums.Count - 1)
      return;

    /* add next and check for duplicates */
    subset.Add(nums[index]);
    if (!alreadyFound(subset))
    {
      List<int> sCopy = new List<int>(subset);
      result.Add(sCopy);
    }

    /* recurse */
    findSubset(nums, index+1, subset);

    /* backtrack - delete last added and recurse again */    
    subset.RemoveAt(subset.Count-1);        
    while (index + 1 < nums.Count)
    {
      findSubset(nums, index+1, subset);
      /* skip over last deleted when re-recursing */
      index++;
    }
  }

  /* check for dupes */
  bool alreadyFound(List<int> s)
  {
    bool found = false;
    List<int> subsetCopy = new List<int>(s);
    subsetCopy.Sort();
    foreach (var r in result)
    {
      if (r.Count != s.Count) continue;
      List<int> rCopy = new List<int>(r);
      rCopy.Sort();
      found = true;
      for (int i = 0; i < r.Count; i++)
        if (rCopy[i] != subsetCopy[i])
          found = false;
      if (found) return true;
    }
    return false;
  }