[Leetcode] convert sorted list to Binary Search Tree

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.

Algorithm ideas:

It is similar to [leetcode] convert sorted array to binary search tree, but there is no essential difference between array and list.

Three steps:

Find the midpoint (speed pointer)

Broken linked list (the precursor to slow pointer needs to be found)

Sub-governance.

 

The Code is as follows:

 1 public class Solution { 2     public TreeNode sortedListToBST(ListNode head) { 3         if(head == null) return null; 4         if(head.next == null) return new TreeNode(head.val); 5         ListNode hhead = new ListNode(0); 6         hhead.next = head; 7         ListNode fast = hhead, slow= hhead; 8         while(fast != null && fast.next != null){ 9             fast = fast.next.next;10             slow = slow.next;11         }12         TreeNode root = new TreeNode(slow.val);13         ListNode right = slow.next;14         ListNode pre = hhead;15         while(pre != null && pre.next != slow){16             pre = pre.next;17         }18         pre.next = null;19         ListNode left = hhead.next;20         root.left = sortedListToBST(left);21         root.right = sortedListToBST(right);22         return root;23     }24 }