Balanced Binary Tree - Leetcode Python Solution

 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:

Given the following tree [3,9,20,null,null,15,7]:

    3
   / \
  9  20
    /  \
   15   7

Return true.

Example 2:

Given the following tree [1,2,2,3,3,null,null,4,4]:

       1
      / \
     2   2
    / \
   3   3
  / \
 4   4

Return false.

   # 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 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 1+max(left,right)
        return check(root) != -1

TC: O(n) SC:O(n)