提供JavaScript版本的《把二叉搜索树转换为累加树》

problems/0538.把二叉搜索树转换为累加树.md

@@ -239,7 +239,70 @@ func RightMLeft(root *TreeNode,sum *int) *TreeNode {
 }
 ```
 
+JavaScript版本
 
+> 递归
+
+```javascript
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {TreeNode}
+ */
+var convertBST = function(root) {
+    let pre = 0;
+    const ReverseInOrder = (cur) => {
+        if(cur) {
+            ReverseInOrder(cur.right);
+            cur.val += pre;
+            pre = cur.val;
+            ReverseInOrder(cur.left);
+        }
+    }
+    ReverseInOrder(root);
+    return root;
+};
+```
+
+> 迭代
+
+```javascript
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {TreeNode}
+ */
+var convertBST = function (root) {
+    let pre = 0;
+    let cur = root;
+    let stack = [];
+    while (cur !== null || stack.length !== 0) {
+        while (cur !== null) {
+            stack.push(cur);
+            cur = cur.right;
+        }
+        cur = stack.pop();
+        cur.val += pre;
+        pre = cur.val;
+        cur = cur.left;
+    }
+    return root;
+};
+```
 
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 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)