diff --git a/problems/0209.长度最小的子数组.md b/problems/0209.长度最小的子数组.md
index fbef7692..ceb06ce9 100644
--- a/problems/0209.长度最小的子数组.md
+++ b/problems/0209.长度最小的子数组.md
@@ -448,6 +448,27 @@ object Solution {
   }
 }
 ```
-
+C#:
+```csharp
+public class Solution {
+    public int MinSubArrayLen(int s, int[] nums) {
+        int n = nums.Length;
+        int ans = int.MaxValue;
+        int start = 0, end = 0;
+        int sum = 0;
+        while (end < n)  {
+            sum += nums[end];
+            while (sum >= s) 
+            {
+                ans = Math.Min(ans, end - start + 1);
+                sum -= nums[start];
+                start++;
+            }
+            end++;
+        }
+        return ans == int.MaxValue ? 0 : ans;
+    }
+}
+```
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