LC110. 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:
        res = [True]
        def dfs(root):
            if root is None:
                return 0
            
            l = dfs(root.left)
            r = dfs(root.right)
 
            if not res[0]:)
                return -1
 
            if abs(l - r) > 1:
                res[0] = False
                return -1
            
            return 1 + max(l, r)
        
        dfs(root)
        return res[0]

Complexity

Time: $O(n)$
Space: $O(n)$