左神算法-二叉树的后继节点和先驱节点【c++实现】

#include 
#include 
using namespace std;

struct Node
{
	int   m_nValue;
	Node* m_pLeft;
	Node* m_pRight;
	Node* m_pParent;
};
//寻找后继节点
Node* most_leftnode(Node* node)
{
	while (node->m_pLeft != nullptr)
		node = node->m_pLeft;
	return node;
}
Node* find_the_next(Node* ptr)
{
	if (ptr == nullptr)
		return ptr;
//如果当前节点的右子树存在，则右子树上最左的节点是后继节点
//否则，若其不为其父节点的左孩子，则向上移动当前节点和其父节点，直到当前节点是其父节点的左孩子
	if (ptr->m_pRight != nullptr) 
		return most_leftnode(ptr->m_pRight);

	Node* parent = ptr->m_pParent;
	while (parent != nullptr&&ptr != parent->m_pLeft)//&&前第一个条件是为了二叉树最右下角节点准备的
	{
		ptr = ptr->m_pParent;
		parent = ptr->m_pParent;
	}
	return parent;
}
//寻找先驱节点
Node* most_rightnode(Node* node)
{
	while (node->m_pRight != nullptr)
		node = node->m_pRight;
	return node;
}
Node* find_the_previous(Node* ptr)
{
	if (ptr == nullptr)
		return ptr;
	//如果当前节点的左子树存在，则左子树上最右的节点是先驱节点
	//否则，若其不为其父节点的右孩子，则向上移动当前节点和其父节点，直到当前节点是其父节点的右孩子
	if (ptr->m_pLeft != nullptr) {
		return most_rightnode(ptr->m_pLeft);
	}else{
		Node* parent = ptr->m_pParent;
		while (parent != nullptr&&ptr != parent->m_pRight)//&&前第一个条件是为了二叉树最左下角的节点准备的
		{
			ptr = ptr->m_pParent;
			parent = ptr->m_pParent;
		}
		return parent;
	}
}

//创建二叉树
Node* create_node(int value)
{
	Node *new_node = new Node;
	new_node->m_nValue = value;
	new_node->m_pLeft = nullptr;
	new_node->m_pRight= nullptr;
	new_node->m_pParent = nullptr;
	return new_node;
}
void ConnectTreeNodes(Node* pParent, Node* pLeft, Node* pRight)
{
	if (pParent != nullptr)
	{
		pParent->m_pLeft = pLeft;
		pParent->m_pRight = pRight;

		if (pLeft != nullptr)
			pLeft->m_pParent = pParent;
		if (pRight != nullptr)
			pRight->m_pParent = pParent;
	}
}

//中序遍历
void in_oeder(Node*head)
{
	stack stack;
	if (head == nullptr)
		return;
	Node *ptr = head;
	Node *tmp = nullptr;
	while (!stack.empty() || ptr != nullptr)
	{
		if (ptr!= nullptr){//注意 判断时不可以拿ptr->next做判断！
			stack.push(ptr);
			ptr = ptr->m_pLeft;
			
		}else{
			tmp = stack.top();
			cout << tmp->m_nValue << endl;
			stack.pop();
			ptr = tmp->m_pRight;
		}
	}
}

int main()
{
	Node* head = create_node(18);
	Node* pNode2 = create_node(26);
	Node* pNode3 = create_node(30);
	Node* pNode4 = create_node(57);
	Node* pNode5 = create_node(78);
	Node* pNode6 = create_node(19);
	Node* pNode7 = create_node(31);

	ConnectTreeNodes(head, pNode2, pNode3);
	ConnectTreeNodes(pNode3, pNode4, pNode5);
	ConnectTreeNodes(pNode5, pNode6, pNode7);

	in_oeder(head);
	Node *search = pNode5;
	cout << "节点" << search->m_nValue << endl;

	if (find_the_next(search) != nullptr) {
		cout << "该节点的后继点是：" << find_the_next(search)->m_nValue << endl;
	}else {
		cout << "该节点的后继点是空：" << endl;
	}

	if (find_the_previous(search) != nullptr) {
		cout << "该节点的先驱点是：" << find_the_previous(search)->m_nValue << endl;
	}
	else {
		cout << "该节点的先驱点是空：" << endl;
	}

	system("pause");
	return 0;
}