Given the head of 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 1:
Input: head = [-10,-3,0,5,9]
Output: [0,-3,9,-10,null,5]
Explanation: One possible answer is [0,-3,9,-10,null,5], which represents the shown height balanced BST.
Example 2:
Input: head = []
Output: []
Constraints:
- The number of nodes in
headis in the range[0, 2 * 104]. -
-105 <= Node.val <= 105
SOLUTION:
# Definition for singly-linked list.
# class ListNode:
# def __init__(self, val=0, next=None):
# self.val = val
# self.next = next
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, val=0, left=None, right=None):
# self.val = val
# self.left = left
# self.right = right
class Solution:
def sortedListToBST(self, head: Optional[ListNode]) -> Optional[TreeNode]:
if not head:
return head
if not head.next:
return TreeNode(val = head.val)
prev = None
slow = head
fast = head
while slow and fast and fast.next:
prev = slow
slow = slow.next
fast = fast.next.next
prev.next = None
root = TreeNode(val = slow.val)
root.left = self.sortedListToBST(head)
root.right = self.sortedListToBST(slow.next)
return root
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