Leetcode 90 Subsets II

Answer:

 public class Solution {  
   public IList<IList<int>> SubsetsWithDup(int[] nums) {  
     List<IList<int>> ret = new List<IList<int>>();  
     if (nums == null)  
     {  
       return ret;  
     }  
     // Have to sort first.  
     Array.Sort(nums);  
     // Create an empty result and add to ret.  
     List<int> start = new List<int>();  
     ret.Add(start);  
     // Resursive backtrack.  
     helper(nums, 0, start, ret);  
     return ret;  
   }  
   void helper(int[] nums, int step, List<int> current, List<IList<int>> ret)  
   {  
     for(int i = step; i < nums.Length; i++)  
     {  
       // Remove dup. The same case has been accounted for in a previous iteration.  
       if (i > step && nums[i] == nums[i-1])  
       {  
         continue;  
       }  
       current.Add(nums[i]);  
       ret.Add(new List<int>(current));  
       helper(nums, i + 1, current, ret);  
       current.RemoveAt(current.Count - 1);  
     }  
   }  
 }