Convert Sorted List to Binary Search Tree.java

/**
 * 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 {
    ListNode cur; 
    public TreeNode sortedListToBST(ListNode head) {
        // Start typing your Java solution below
        // DO NOT write main() function
        int length=lengthOfList(head);
        cur=head;
        return BST(0, length-1);
    }
    TreeNode BST(int start, int end)
    {
        if(start>end) return null; 
        int mid=start+(end-start)/2;
        TreeNode left=BST( start, mid-1);
        TreeNode parent=new TreeNode(cur.val); 
        parent.left=left; 
        cur=cur.next; 
        parent.right=BST(mid+1, end );
        return parent; 
    }
    int lengthOfList(ListNode head)
    {
        int counter=0; 
        ListNode current=head;
        while(current!=null)
        {
            counter++; current=current.next; 
        }
        return counter; 
    }
}