173. 二叉搜索树迭代器

Author: w2xi

README.md

@@ -74,6 +74,7 @@
 |151|[颠倒字符串中的单词](https://leetcode.cn/problems/reverse-words-in-a-string/)|[JavaScript](./algorithms/reverse-words-in-a-string.js)|Medium|
 |155|[最小栈](https://leetcode.cn/problems/min-stack/)|[JavaScript](./algorithms/min-stack.js)|Easy|
 |160|[相交链表](https://leetcode.cn/problems/intersection-of-two-linked-lists/)|[JavaScript](./algorithms/intersection-of-two-linked-lists.js)|Easy|
+|173|[二叉搜索树迭代器](https://leetcode.cn/problems/binary-search-tree-iterator/)|[JavaScript](./algorithms/binary-search-tree-iterator.js)|Medium|
 |189|[轮转数组](https://leetcode-cn.com/problems/rotate-array/)|[JavaScript](./algorithms/rotate-array.js)|Medium|
 |199|[二叉树的右视图](https://leetcode.cn/problems/binary-tree-right-side-view/)|[JavaScript](./algorithms/binary-tree-right-side-view.js)|Medium|
 |202|[快乐数](https://leetcode.cn/problems/happy-number/)|[JavaScript](./algorithms/happy-number.js)|Easy|

algorithms/binary-search-tree-iterator.js

@@ -0,0 +1,56 @@
+/**
+ * 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
+ */
+var BSTIterator = function (root) {
+  let prev = null;
+  let head = null;
+  // 中序遍历
+  // 二叉搜索树 => 链表
+  const toLinkedList = (root) => {
+    if (!root) return null;
+    toLinkedList(root.left);
+    if (prev) {
+      prev.right = root;
+    } else {
+      head = root;
+    }
+    root.left = null;
+    prev = root;
+    toLinkedList(root.right);
+  };
+  toLinkedList(root);
+  this.head = head;
+  const dummyNode = new TreeNode(-1);
+  dummyNode.right = head;
+  this.curr = dummyNode;
+};
+
+/**
+ * @return {number}
+ */
+BSTIterator.prototype.next = function () {
+  this.curr = this.curr.right;
+  return this.curr.val;
+};
+
+/**
+ * @return {boolean}
+ */
+BSTIterator.prototype.hasNext = function () {
+  return !!this.curr.right;
+};
+
+/**
+ * Your BSTIterator object will be instantiated and called as such:
+ * var obj = new BSTIterator(root)
+ * var param_1 = obj.next()
+ * var param_2 = obj.hasNext()
+ */