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110.balanced-binary-tree.py
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55 lines (48 loc) · 1.11 KB
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# Tag: Tree, Depth-First Search, Binary Tree
# Time: O(N)
# Space: O(H)
# Ref: -
# Note: Recursion
# Given a binary tree, determine if it is height-balanced.
#
# Example 1:
#
#
# Input: root = [3,9,20,null,null,15,7]
# Output: true
#
# Example 2:
#
#
# Input: root = [1,2,2,3,3,null,null,4,4]
# Output: false
#
# Example 3:
#
# Input: root = []
# Output: true
#
#
# Constraints:
#
# The number of nodes in the tree is in the range [0, 5000].
# -104 <= Node.val <= 104
#
#
# 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 isBalanced(self, root: Optional[TreeNode]) -> bool:
return self.helper(root) != -1
def helper(self, node: Optional[TreeNode]) -> int:
if node is None:
return 0
left = self.helper(node.left)
right = self.helper(node.right)
if left == -1 or right == -1 or abs(left - right) > 1:
return -1
return max(left, right) + 1