110. Balanced Binary Tree-平衡二叉树

Given a binary tree, determine if it is height-balanced.

For this problem, a height-balanced binary tree is defined as:

a binary tree in which the left and right subtrees of every node differ in height by no more than 1.

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].
• -10^4 <= Node.val <= 10^4

Solution in python:

# 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: TreeNode) -> bool:

        def Height(root: TreeNode):
            if root == None:
                return 0
            else:
                return 1 + max(Height(root.left), Height(root.right))

        if root == None:
            return True
        elif abs(Height(root.left) - Height(root.right)) <= 1:
                return self.isBalanced(root.left) and self.isBalanced(root.right)
        else:
            return False