Convert Sorted List to Binary Search Tree

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

Solution:

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
/**
 * Definition for a binary tree node.
 * 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;
        if(head.next==null) return new TreeNode(head.val);
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode slow = dummy, fast = dummy, pre = dummy;
        while(fast!=null && fast.next!=null){
            pre = slow;
            slow = slow.next;
            fast = fast.next.next;
        }
        pre.next = null;
        TreeNode root = new TreeNode(slow.val);
        root.left = sortedListToBST(dummy.next);
        root.right = sortedListToBST(slow.next);
        return root;
    }
}