Update0112.路径总和，添加C#递归版

problems/0112.路径总和.md

@@ -1511,6 +1511,17 @@ impl Solution {
     }
 }
 
+```
+### C#
+```C#
+// 0112.路径总和
+// 递归 
+public bool HasPathSum(TreeNode root, int targetSum)
+{
+    if (root == null) return false;
+    if (root.left == null && root.right == null && targetSum == root.val) return true;
+    return HasPathSum(root.left, targetSum - root.val) || HasPathSum(root.right, targetSum - root.val);
+}
 ```
 
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