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Check If a Tree Is Balanced

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Problem

MSCI analytics services can represent hierarchical structures as binary trees. Given the root of a binary tree, determine whether the tree is height-balanced.

A binary tree is height-balanced when, for every node, the heights of its left and right subtrees differ by no more than 1.

Formal Specification

Implement is_balanced(root), where root is either None or a nested dictionary with this structure:

  • value: an integer node value
  • left: another node dictionary or None
  • right: another node dictionary or None

Return True if the tree is height-balanced, otherwise return False. The values do not affect the result.

Your solution should avoid repeatedly calculating subtree heights. Use a depth-first strategy that detects imbalance while returning height information to each parent.

Constraints

  • The tree contains between 0 and 10^5 nodes.
  • Each node has at most two children.
  • Node values are integers in the range [-10^9, 10^9].
  • None represents an empty subtree.

Function Signature

def is_balanced(root):
Your solutionPython 3
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