diff --git a/problems/0704.二分查找.md b/problems/0704.二分查找.md
index 379cb5fc..15e096a0 100644
--- a/problems/0704.二分查找.md
+++ b/problems/0704.二分查找.md
@@ -561,5 +561,51 @@ class Solution {
 }
 ```
 
+**C#:**
+```csharp
+//左闭右闭
+public class Solution {  
+    public int Search(int[] nums, int target) {
+        int left = 0;
+        int right = nums.Length - 1;
+        while(left <= right){
+            int mid = (right - left ) / 2 + left;
+            if(nums[mid] == target){
+                return mid;
+            }
+            else if(nums[mid] < target){
+                left = mid+1;
+            }
+            else if(nums[mid] > target){
+                right = mid-1;
+            }
+        }
+        return -1;
+    }
+}
+
+//左闭右开
+public class Solution{
+    public int Search(int[] nums, int target){
+        int left = 0;
+        int right = nums.Length;
+        while(left < right){
+            int mid = (right - left) / 2 + left;
+            if(nums[mid] == target){
+                return mid;
+            }
+            else if(nums[mid] < target){
+                left = mid + 1;
+            }
+            else if(nums[mid] > target){
+                right = mid;
+            }
+        }
+        return -1;
+    }
+}
+```
+
+
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 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>