balanced_binary_tree.cpp

/*
110. Balanced Binary Tree
Easy

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
*/

/**
 * 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 {
public:
    
    int height(TreeNode* root){
        if(root==NULL)
            return 0;
        return max(height(root->left), height(root->right))+1;
    }

    bool isBalanced(TreeNode* root) {
        if(root == NULL)
            return true;
        if(abs(height(root->left) - height(root->right))>1)
            return false;
        return isBalanced(root->left) && isBalanced(root->right);
    }
};