LeetCode: Maximum Depth of Binary Tree

int maxDepth(TreeNode *root)
{
	if (root == NULL) return 0;
	int left = maxDepth1(root->left);
	int right = maxDepth1(root->right);
	return left > right ? left + 1 : right + 1;
}

int maxDepth(TreeNode *root)
{
	if (root == NULL) return 0;
	queue<TreeNode *>  btQueue;//使用队列进行层序遍历
	btQueue.push(root);
	int count = 1;//记录当前层的节点个数
	int depth = 0;//记录当前遍历的深度
	while (!btQueue.empty())
	{
		TreeNode *currentNode = btQueue.front();
		btQueue.pop();//每次循环出队一个节点
		count--;

		if (currentNode->left) btQueue.push(currentNode->left);
		if (currentNode->right) btQueue.push(currentNode->right);

		if (count == 0)
		{
			//每当遍历完上一次节点的时候，层数depth++，count修改为现在队列中的元素个数，即下层的节点个数
			depth++;
			count = btQueue.size();
		}
	}
	return depth;
}