22. Balanced Binary Tree.cpp

/*
Balanced Binary Tree
====================

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].
-104 <= Node.val <= 104
*/

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */

class Solution
{
  int height(TreeNode *root)
  {
    if (!root)
      return 0;
    auto left = height(root->left);
    auto right = height(root->right);
    return max(left, right) + 1;
  }

public:
  bool isBalanced(TreeNode *root)
  {
    if (!root)
      return true;
    return isBalanced(root->left) && isBalanced(root->right) && abs(height(root->left) - height(root->right)) <= 1;
  }
};