create 0047-permutations-ii.cs

Author: NotADucc

Diff for: csharp/0047-permutations-ii.cs

@@ -0,0 +1,34 @@
+public class Solution
+{
+    public IList<IList<int>> PermuteUnique(int[] nums)
+    {
+        Array.Sort(nums);
+        var output = new List<IList<int>>();
+        Backtrack(output, nums.ToList(), []);
+        return output;
+    }
+
+    private void Backtrack(List<IList<int>> output, List<int> nums, List<int> current)
+    {
+        if (nums.Count == 0)
+        {
+            output.Add(new List<int>(current));
+        }
+        else
+        {
+            for (int i = 0; i < nums.Count; i++)
+            {
+                if (i > 0 && nums[i] == nums[i - 1])
+                {
+                    continue;
+                }
+                int num = nums[i];
+                current.Add(num);
+                nums.Remove(num);
+                Backtrack(output, nums, current);
+                nums.Insert(i, num);
+                current.RemoveAt(current.Count - 1);
+            }
+        }
+    }
+}