Update 0047.全排列2，添加C#

problems/0047.全排列II.md

@@ -521,6 +521,38 @@ object Solution {
   }
 }
 ```
+### C#
+```csharp
+public class Solution
+{
+    public List<IList<int>> res = new List<IList<int>>();
+    public List<int> path = new List<int>();
+    public IList<IList<int>> PermuteUnique(int[] nums)
+    {
+        Array.Sort(nums);
+        BackTracking(nums, new bool[nums.Length]);
+        return res;
+    }
+    public void BackTracking(int[] nums, bool[] used)
+    {
+        if (nums.Length == path.Count)
+        {
+            res.Add(new List<int>(path));
+            return;
+        }
+        for (int i = 0; i < nums.Length; i++)
+        {
+            if (i > 0 && nums[i] == nums[i - 1] && used[i - 1] == false) continue;
+            if (used[i]) continue;
+            path.Add(nums[i]);
+            used[i] = true;
+            BackTracking(nums, used);
+            path.RemoveAt(path.Count - 1);
+            used[i] = false;
+        }
+    }
+}
+```
 
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