LeetCode: 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

public TreeNode sortedListToBST(ListNode head) {
    if (head == null) return null;
    if (head.next == null) return new TreeNode(head.val);

    ListNode fast, slow, preSlow;
    fast = slow = preSlow = head;
    while (fast.next != null && fast.next.next != null) {
        preSlow = slow;
        slow = slow.next;
        fast = fast.next.next;
    }

    fast = slow.next;
    preSlow.next = null;
    TreeNode node = new TreeNode(slow.val);
    if (slow != head) node.left = sortedListToBST(head);
    node.right = sortedListToBST(fast);
    return node;
}