Problem
Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST.
For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.
Example:
Given the sorted linked list: [-10,-3,0,5,9],
One possible answer is: [0,-3,9,-10,null,5], which represents the following height balanced BST:
0 / -3 9 / / -10 5Solution
class Solution { public TreeNode sortedListToBST(ListNode head) { return helper(head, null); } private TreeNode helper(ListNode head, ListNode tail) { if (head == tail) return null; ListNode fast = head, slow = head; while (fast != tail && fast.next != tail) { fast = fast.next.next; slow = slow.next; } TreeNode root = new TreeNode(slow.val); root.left = helper(head, slow); root.right = helper(slow.next, tail); return root; } }
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