109. Convert Sorted List to Binary Search Tree

https://leetcode.com/problems/convert-sorted-list-to-binary-search-tree/discuss/35476/Share-my-JAVA-solution-1ms-very-short-and-concise.

 

 1 class Solution {
 2     public TreeNode sortedListToBST(ListNode head) {
 3         return helper(head, null);
 4         
 5     }
 6     
 7     public TreeNode helper(ListNode head, ListNode last) {
 8         if(head == last) {
 9             return null;
10         }
11         ListNode slow = head;
12         ListNode fast = head;
13         while(fast.next != last && fast.next.next != last) { // 这里是不等于last
14             fast = fast.next.next;
15             slow = slow.next;
16         }
17         TreeNode root = new TreeNode(slow.val);
18         root.left = helper(head, slow);
19         root.right = helper(slow.next, last);
20         return root;
21     }
22     
23 }

 

posted @ 2018-09-20 10:29  jasoncool1  阅读(99)  评论(0)  编辑  收藏  举报