Definition for a binary tree node.
Definition for a binary tree node.

Definition for a binary tree node.

Solved at: 220925

Question

Given a binary tree, determine if it is height-balanced.

For this problem, a height-balanced binary tree is defined as:

a binary tree in which the left and right subtrees of every node differ in height by no more than 1.

Solution

python
# 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 = rightclass Solution:
    def getHeight(self, node):        if node == None:            return 0        l = node.left        r = node.right        return max(self.getHeight(l), self.getHeight(r)) + 1
    def isBalanced(self, root: Optional[TreeNode]) -> bool:        if root == None:            return True        l = root.left        r = root.right        lh = self.getHeight(l)        rh = self.getHeight(r)        return abs(lh - rh) <= 1 and self.isBalanced(l) and self.isBalanced(r)

Results

Runtime

  • 123 ms, faster than14.05%ofPython3online submissions forBalanced Binary Tree.

Memory Usage

  • 18.6 MB, less than90.53%ofPython3online submissions forBalanced Binary Tree.

Complexity Analysis

Time

  • $O(n \log n)$ because worst case, we might need to travel all nodes while counting their height with $O(n)$

Space

  • $O(n)$ because we require a stack to contain all nodes, worst case.

Other Answers Online

Backlinks (2)
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# 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 = rightclass Solution:
    def getHeight(self, node):        if node == None:            return 0        l = node.left        r = node.right        return max(self.getHeight(l), self.getHeight(r)) + 1
    def isBalanced(self, root: Optional[TreeNode]) -> bool:        if root == None:            return True        l = root.left        r = root.right        lh = self.getHeight(l)        rh = self.getHeight(r)        return abs(lh - rh) <= 1 and self.isBalanced(l) and self.isBalanced(r)