int maxDepth(TreeNode *root) {
    if(!root) return 0;
    return max(maxDepth(root->left), maxDepth(root->right)) + 1;
}

bool isBalanced(TreeNode* root) {
    if(!root) return true;
    int leftHeight = maxDepth(root->left);
    int rightHeight = maxDepth(root->right);
    return abs(leftHeight - rightHeight) <= 1 && isBalanced(root->left) && isBalanced(root->right);
}