Balanced binary tree

# 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:
        flag = [True]
        def dfs(node):
            if not node:
                return -1
            left = dfs(node.left)
            right = dfs(node.right)
            if abs(left - right) > 1:
                flag[0] = False
            return 1 + max(left, right)

        dfs(root)
        return flag[0]

Balanced Binary Tree

Difficulty: Easy

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