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 5
class Solution {
public TreeNode sortedListToBST(ListNode head) {
if(head == null) return null;
return toBST(head,null);
}
private TreeNode toBST(ListNode head, ListNode tail){
ListNode slow = head;
ListNode fast = head;
if(head == tail) return null;
while(fast != tail && fast.next != tail){
fast = fast.next.next;
slow = slow.next;
}
TreeNode root = new TreeNode(slow.val);
root.left = toBST(head, slow);
root.right = toBST(slow.next, tail);
return root;
}
}