C语言进阶练习二叉树的递归遍历

// 二叉树前序遍历
void PreOrder(BTnode* root)
{
	if (root == nullptr)
	{
		cout << "# ";
		return;       // 空的话结束递归，输出#来表示这是一个空结点
	}
	cout << root->data << " ";
	PreOrder(root->left);
	PreOrder(root->right);
}
// 二叉树中序遍历
void InOrder(BTNode* root)
{
	if (root == nullptr)
	{
		cout << "# ";
		return;
	}
	InOrder(root->left);
	cout << root->data << " ";
	InOrder(root->right);
}
// 二叉树后序遍历
void PostOrder(BTNode* root)
{
	if (root == nullptr)
	{
		cout << "# ";
		return;
	}
	PostOrder(root->left);
	PostOrder(root->right);
	cout << root->data << " ";
}

int count = 0;
void TreeSize1(BTNode* root)
{
	if (root == nullptr)
		return;
	++::count;
	TreeSize1(root->left);
	TreeSize1(root->right);
}
int TreeSize2(BTNode* root)
{
	if (root == NULL)
		return 0;
	return 1 + TreeSize2(root->left) + TreeSize2(root->right);
}

int LeafTreeNode(BTNode* root)
{
	if (root == nullptr)
	{
		return 0;
	}
	else if (root->left == NULL && root->right == NULL)
	{
		return 1;
	}
	else
	{
		return LeafTreeNode(root->left) + LeafTreeNode(root->right);
	}
}

int TreeKLevel(BTNode* root, int k)   //求第k层
{
	if (root == NULL)
		return 0;
	if (k == 1)
		return 1;
	return TreeKLevel(root->left, k - 1) + TreeKLevel(root->right, k - 1);
}

BTNode* TreeFind(BTNode* root, BTDataType x)
{
	if (root == NULL)
		return NULL;
	if (root->data == x)
		return root;
	BTNode* retleft = TreeFind(root->left, x);
	if (retleft)
		return retleft;
	BTNode* retright = TreeFind(root->right, x);
	if (retright)
		return retright;
	return NULL;
}

int  TreeDepth(BTNode* root)
{
	if (root == NULL)
		return 0;
	int leftdepth = TreeDepth(root->left);
	int rightdepth = TreeDepth(root->right);
	return 1 + leftdepth > rightdepth ? leftdepth : rightdepth;
}