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

标题：	Convert Sorted List to Binary Search Tree
通过率：	27.8%
难度：	中等

Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST.

本题难度就是链表的随机查找，那么不停的将链表拆分成两条，然后递归调用。代码如下：

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; next = null; }
 * }
 */
/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public TreeNode sortedListToBST(ListNode head) {
        if(head==null)return null;
        ListNode h=head;
        int len=0;
        while(h!=null){
            len++;
            h=h.next;
        }
        return creattree(head,0,len-1);
        
    }
    public TreeNode creattree(ListNode head,int start,int end){
        if(start>end)return null;
        int mid=(start+end)/2;
        ListNode tmp=head;
        for(int i=start;i<mid;i++){
            head=head.next;
        }
        TreeNode root=new TreeNode(head.val);
        root.left=creattree(tmp,start,mid-1);
        root.right=creattree(head.next,mid+1,end);
        return root;
        
        
    }
}