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convert-sorted-list-to-binary-search-tree.py
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convert-sorted-list-to-binary-search-tree.py
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from __future__ import print_function
# Time: O(n)
# Space: O(logn)
#
# Given a singly linked list where elements are sorted in ascending order,
# convert it to a height balanced BST.
#
# Definition for a binary tree node
class TreeNode:
def __init__(self, x):
self.val = x
self.left = None
self.right = None
#
# Definition for singly-linked list.
class ListNode:
def __init__(self, x):
self.val = x
self.next = None
class Solution:
head = None
# @param head, a list node
# @return a tree node
def sortedListToBST(self, head):
current, length = head, 0
while current is not None:
current, length = current.next, length + 1
self.head = head
return self.sortedListToBSTRecu(0, length)
def sortedListToBSTRecu(self, start, end):
if start == end:
return None
mid = start + (end - start) / 2
left = self.sortedListToBSTRecu(start, mid)
current = TreeNode(self.head.val)
current.left = left
self.head = self.head.next
current.right = self.sortedListToBSTRecu(mid + 1, end)
return current
if __name__ == "__main__":
head = ListNode(1)
head.next = ListNode(2)
head.next.next = ListNode(3)
result = Solution().sortedListToBST(head)
print(result.val)
print(result.left.val)
print(result.right.val)