2026-02-08 10:23:59 +0000 UTC

# 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:
        return self.dfs(root) != -1

    def dfs(self, node: Optional[TreeNode]) -> int:
        if node is None:
            return 0
        depth1, depth2 = self.dfs(node.left), self.dfs(node.right)
        if depth1 == -1 or depth2 == -1 or abs(depth2 - depth1) > 1:
            return -1
        return 1 + max(depth1, depth2)