diff --git a/problems/0538.把二叉搜索树转换为累加树.md b/problems/0538.把二叉搜索树转换为累加树.md
index 6de98c6f..16b00817 100644
--- a/problems/0538.把二叉搜索树转换为累加树.md
+++ b/problems/0538.把二叉搜索树转换为累加树.md
@@ -293,6 +293,27 @@ var convertBST = function (root) {
 };
 ```
 
+##C
+
+递归
+```c
+int pre;
+void traversal(struct TreeNode* node) {
+    if(!node)
+        return ;
+    traversal(node->right);
+    node->val = node->val + pre;
+    pre = node->val;
+    traversal(node->left);
+}
+
+struct TreeNode* convertBST(struct TreeNode* root){
+    pre = 0;
+    traversal(root);
+    return root;
+}
+```
+
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)
 * B站视频：[代码随想录](https://space.bilibili.com/525438321)