Balanced Binary Tree

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.

 

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

SOLUTION:

# 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 getHeight(self, root):
        if root:
            a = self.getHeight(root.left)
            b = self.getHeight(root.right)
            return 1 + max(a, b)
        return -1
    
    def isBalanced(self, root: Optional[TreeNode]) -> bool:
        if root:
            a = self.getHeight(root.left)
            b = self.getHeight(root.right)
            if abs(a - b) <= 1 and self.isBalanced(root.left) and self.isBalanced(root.right):
                return True
            return False
        else:
            return True