leetcode——110. 平衡二叉树

class Solution:
    def isBalanced(self, root: TreeNode) -> bool:
        if not root:
            return True
        def helper(node):
            if not node:
                return 0
            left=helper(node.left)
            right=helper(node.right)
            return max(left,right)+1
        return abs(helper(root.left)-helper(root.right))<=1 and self.isBalanced(root.left) and self.isBalanced(root.right)