leetcode------Convert Sorted List to Binary Search Tree

 1 /**
 2  * Definition for singly-linked list.
 3  * public class ListNode {
 4  *     int val;
 5  *     ListNode next;
 6  *     ListNode(int x) { val = x; next = null; }
 7  * }
 8  */
 9 /**
10  * Definition for binary tree
11  * public class TreeNode {
12  *     int val;
13  *     TreeNode left;
14  *     TreeNode right;
15  *     TreeNode(int x) { val = x; }
16  * }
17  */
18 public class Solution {
19     public TreeNode sortedListToBST(ListNode head) {
20         if(head==null)return null;
21         ListNode h=head;
22         int len=0;
23         while(h!=null){
24             len++;
25             h=h.next;
26         }
27         return creattree(head,0,len-1);
28         
29     }
30     public TreeNode creattree(ListNode head,int start,int end){
31         if(start>end)return null;
32         int mid=(start+end)/2;
33         ListNode tmp=head;
34         for(int i=start;i<mid;i++){
35             head=head.next;
36         }
37         TreeNode root=new TreeNode(head.val);
38         root.left=creattree(tmp,start,mid-1);
39         root.right=creattree(head.next,mid+1,end);
40         return root;
41         
42         
43     }
44 }