Update0491.递增子序列，添加C#

problems/0491.递增子序列.md

@@ -614,6 +614,32 @@ object Solution {
   }
 }
 ```
+### C#
+```csharp
+public class Solution {
+    public IList<IList<int>> res = new List<IList<int>>();
+    public IList<int> path = new List<int>();
+    public IList<IList<int>> FindSubsequences(int[] nums) {
+        BackTracking(nums, 0);
+        return res;
+    }
+    public void BackTracking(int[] nums, int start){
+        if(path.Count >= 2){
+            res.Add(new List<int>(path));
+        }
+        HashSet<int> hs = new HashSet<int>();
+        for(int i = start; i < nums.Length; i++){
+            if(path.Count > 0 && path[path.Count - 1] > nums[i] || hs.Contains(nums[i])){
+                continue;
+            }
+            hs.Add(nums[i]);
+            path.Add(nums[i]);
+            BackTracking(nums, i + 1);
+            path.RemoveAt(path.Count - 1);
+        }
+    }
+}
+```
 
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