balanced-binary-tree.py

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def isBalanced(self, root):
        
        def check(root):
            if not root: return 0
            left = check(root.left)
            right = check(root.right)
            if left == -1 or right == -1 or abs(left - right) > 1:
                return -1
            return max(left, right) + 1
        
        return check(root) != -1
            
        return check(root) != -1