Update0040.组合总和2，添加C#

problems/0040.组合总和II.md

@@ -773,7 +773,39 @@ 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>> CombinationSum2(int[] candidates, int target)
+    {
 
+        Array.Sort(candidates);
+        BackTracking(candidates, target, 0, 0);
+        return res;
+    }
+    public void BackTracking(int[] candidates, int target, int start, int sum)
+    {
+        if (sum > target) return;
+        if (sum == target)
+        {
+            res.Add(new List<int>(path));
+            return;
+        }
+        for (int i = start; i < candidates.Length && sum + candidates[i] <= target; i++)
+        {
+            if (i > start && candidates[i] == candidates[i - 1]) continue;
+            sum += candidates[i];
+            path.Add(candidates[i]);
+            BackTracking(candidates, target, i + 1, sum);
+            sum -= candidates[i];
+            path.RemoveAt(path.Count - 1);
+        }
+    }
+}
+```
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