Convert Sorted List to BST — Fast/Slow + Recursion

# Python
def sortedListToBST(head):
    if not head: return None
    if not head.next: return TreeNode(head.val)
    # Find middle and disconnect left half
    slow = head; fast = head; prev = None
    while fast and fast.next:
        prev = slow; slow = slow.next; fast = fast.next.next
    if prev: prev.next = None  # disconnect left half
    root = TreeNode(slow.val)
    root.left = sortedListToBST(head if prev else None)
    root.right = sortedListToBST(slow.next)
    return root

// Java
public TreeNode sortedListToBST(ListNode head) {
    if (head == null) return null;
    if (head.next == null) return new TreeNode(head.val);
    ListNode slow = head, fast = head, prev = null;
    while (fast != null && fast.next != null) {
        prev = slow; slow = slow.next; fast = fast.next.next;
    }
    if (prev != null) prev.next = null;
    TreeNode root = new TreeNode(slow.val);
    root.left = sortedListToBST(prev != null ? head : null);
    root.right = sortedListToBST(slow.next);
    return root;
}