[leetcode] 110. Balanced Binary Tree

Givin a binary tree, determine if it is 

height-balanced

.

 

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].
• -104 <= Node.val <= 104

 

# 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:
        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