Check is a binary tree is balanced.

tree_is_balanced.cpp

template<typename T>
std::pair<bool, std::size_t> _tree_is_balanced(const TreeNode<T>* node)
{
	if (! node) return {true, 0};
	
	auto left = _tree_is_balanced(node->left);
	
	if (! left.first) return {false, 0};
	
	auto right = _tree_is_balanced(node->right);
	
	if (! right.first) return {false, 0};
	
	if (std::abs<std::size_t>(left.second - right.second) > 1)
	{
		return {false, 0};
	}
	
	else return {true, left.second + 1 + right.second};
}

template<typename T>
bool tree_is_balanced(const TreeNode<T>* root)
{
	return _tree_is_balanced(root).first;
}