109. 有序链表转换二叉搜索树

Author: w2xi

README.md

@@ -53,6 +53,7 @@
 |106|[从中序与后序遍历序列构造二叉树](https://leetcode.cn/problems/construct-binary-tree-from-inorder-and-postorder-traversal/)|[JavaScript](./algorithms/construct-binary-tree-from-inorder-and-postorder-traversal.js)|Medium|
 |107|[二叉树的层序遍历 II](https://leetcode.cn/problems/binary-tree-level-order-traversal-ii/)|[JavaScript](./algorithms/binary-tree-level-order-traversal-ii.js)|Medium|
 |108|[将有序数组转换为二叉搜索树](https://leetcode.cn/problems/convert-sorted-array-to-binary-search-tree/)|[JavaScript](./algorithms/convert-sorted-array-to-binary-search-tree.js)|Easy|
+|109|[有序链表转换二叉搜索树](https://leetcode.cn/problems/convert-sorted-list-to-binary-search-tree/)|[JavaScript](./algorithms/convert-sorted-list-to-binary-search-tree.js)|Medium|
 |110|[平衡二叉树](https://leetcode.cn/problems/balanced-binary-tree/)|[JavaScript](./algorithms/balanced-binary-tree.js)|Easy|
 |111|[二叉树的最小深度](https://leetcode.cn/problems/minimum-depth-of-binary-tree/)|[JavaScript](./algorithms/minimum-depth-of-binary-tree.js)|Easy|
 |112|[路径总和](https://leetcode.cn/problems/path-sum/)|[JavaScript](./algorithms/path-sum.js)|Easy|

algorithms/convert-sorted-list-to-binary-search-tree.js

@@ -0,0 +1,42 @@
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val, next) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.next = (next===undefined ? null : next)
+ * }
+ */
+/**
+ * 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 {ListNode} head
+ * @return {TreeNode}
+ */
+var sortedListToBST = function (head) {
+  if (!head) return null;
+  if (!head.next) return new TreeNode(head.val);
+
+  let slow = head;
+  let fast = head;
+  // 左边的最后一个节点
+  let lastLeft = head;
+  // 快慢指针找到中间节点
+  while (fast && fast.next) {
+    lastLeft = slow;
+    slow = slow.next;
+    fast = fast.next.next;
+  }
+  const right = slow.next;
+  slow.next = null;
+  lastLeft.next = null;
+  const root = new TreeNode(slow.val);
+  root.left = sortedListToBST(head);
+  root.right = sortedListToBST(right);
+
+  return root;
+};