<p>Given a binary tree, determine if it is <span data-keyword="height-balanced"><strong>height-balanced</strong></span>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/10/06/balance_1.jpg" style="width: 342px; height: 221px;" />
<pre>
<strong>Input:</strong> root = [3,9,20,null,null,15,7]
<strong>Output:</strong> true
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/10/06/balance_2.jpg" style="width: 452px; height: 301px;" />
<pre>
<strong>Input:</strong> root = [1,2,2,3,3,null,null,4,4]
<strong>Output:</strong> false
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> root = []
<strong>Output:</strong> true
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The number of nodes in the tree is in the range <code>[0, 5000]</code>.</li>
	<li><code>-10<sup>4</sup> &lt;= Node.val &lt;= 10<sup>4</sup></code></li>
</ul>

# 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:
#         return self.getHight(root) != -1

#     def getHight(self, node):
#         if not node:
#             return 0
#         leftHeight = self.getHight(node.left)
#         rightHeight = self.getHight(node.right)
#         if leftHeight == -1 or rightHeight == -1 or abs(leftHeight - rightHeight) > 1:
#             return -1
#         return max(leftHeight, rightHeight) + 1

class Solution:
    def isBalanced(self, root: Optional[TreeNode]) -> bool:
        if not root:
            return True
        
        height_map = {}
        stack = [root]
        while stack:
            node = stack.pop()
            if node:
                stack.append(node)
                stack.append(None)
                if node.left: stack.append(node.left)
                if node.right: stack.append(node.right)
            else:
                real_node = stack.pop()
                left, right = height_map.get(real_node.left, 0), height_map.get(real_node.right, 0)
                if abs(left - right) > 1:
                    return False
                height_map[real_node] = 1 + max(left, right)
        return True
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