链表篇（一）

链表篇

#include<stdio.h>
//测试数据
const int arrrlens = 9;
int arr[arrrlens] = { 0, 1, 2, 3, 4, 5, 6, 7, 8 };

class Node {
public:
	//构造函数，创建一个节点
	Node(int el = 0, Node * ptr = NULL) {
		infor = el;
		next = ptr;
	}
	int infor;
	Node* next;
};
class NodeList {
public:
	NodeList() {
		head = tail = NULL;
	}
	~NodeList() {
		delete head;
		delete tail;
	}
	//节点插入头部
	void printList();
	void addToHead(int);
	void addLoop(int);
	Node* deleteFromHead(int);
	int insertNode(int);
	Node* findKthTail(Node*, int);
	Node* findKthTail2(Node*, int);
	int isExistLoop();
	int LoopLength();
	Node* getEntryNodeOfLoop();
public:
	Node* head, * tail;
};

void NodeList::addToHead(int node)
{
	Node* p = new Node(node, NULL);
	p->next = head;
	head = p;
}
//添加环
void NodeList::addLoop(int node)
{
	Node* p = head, * end = NULL;
	Node* loop_start = NULL;
	while (p->next != NULL)
	{
		if (p->infor == node)
			loop_start = p;
		p = p->next;
	}
	p->next = loop_start;
}
//要考虑所有条件
Node* NodeList::deleteFromHead(int node)
{
	Node* p = head, * q = head;
	if (head == NULL)
		return head;
	if (p->infor == node)
	{
		q = head;
		head = head->next;
		delete q;
		return head;
	}
	while (p->next != NULL)
	{
		if (p->next->infor == node)
		{
			q = p->next;
			p->next = p->next->next;
			delete q;
			break;
		}
		p = p->next;
	}
	if (p->next == NULL)
		printf("not find node...\n");
	return head;
}
//插入节点
int NodeList::insertNode(int node)
{
	Node* p = head;
	Node* inode = new Node(node);
	if (p->infor <= node)
	{
		inode->next = head->next;
		head->next = inode;
		return 0;
	}
	while (p->next != NULL)
	{
		if (p->next->infor <= node)
		{
			inode->next = p->next->next;
			p->next = inode;
			return 0;
		}
		p = p->next;
	}
	return 0;
}
//find the kth Tail 使用递归
int num = 0;
Node* NodeList::findKthTail(Node* phead, int k)
{
	num = k;
	if (phead == NULL)
		return NULL;
	Node* pCur = findKthTail(phead->next, k);
	if (pCur != NULL)
		return pCur;
	else {
		num--;
		if (num == 0)
			return phead;
		return NULL;
	}
}
//双指针法 find the kth Tail
Node* NodeList::findKthTail2(Node* phead, int k)
{
	Node* p = head, * q = head;
	if (head == NULL || k == 0)
		return NULL;
	while (q != NULL && k)
	{
		q = q->next;
		k--;
	}
	while (q != NULL)
	{
		p = p->next;
		q = q->next;
	}
	if (k > 0)
		return NULL;
	return p;
}
//判断是否为环
int NodeList::isExistLoop()
{
	Node* slow = head, * fast = head;
	//到结尾两个指针相遇
	while (slow != NULL && fast->next != NULL)
	{
		slow = slow->next;
		fast = fast->next->next;
		if (slow == fast)
			return 1;
	}
	return 0;
}
//计算环的长度，找到第二次相遇点即可
int NodeList::LoopLength()
{
	Node* slow = head, * fast = head;
	int count = 1;
	while (slow != NULL && fast->next != NULL)
	{
		slow = slow->next;
		fast = fast->next->next;
		if (slow == fast)
			break;
	}
	slow = slow->next;
	fast = fast->next->next;
	while (slow != fast)
	{
		slow = slow->next;
		fast = fast->next->next;
		count++;

	}
	return count;
}
//得到环的入口节点
Node* NodeList::getEntryNodeOfLoop()
{
	Node* meetingNode = NULL;
	Node* slow = head, * fast = head;
	//到结尾两个指针相遇
	while (slow != NULL && fast->next != NULL)
	{
		slow = slow->next;
		fast = fast->next->next;
		if (slow == fast)
		{
			meetingNode = fast;
			break;
		}
	}
	Node* p1 = head, *p2 = meetingNode;
	while (p1 != p2 )
	{
		p1 = p1->next;
		p2 = p2->next;
	}
	printf("Entry Node of Loop: %d \n", p1->infor);
	return p1;
}

void NodeList::printList()
{
	Node* p = head;
	int count = 0;
	while (p != NULL && count < arrrlens)
	{
		printf("%d ", p->infor);
		p = p->next;
		count++;
	}
	printf("\n");
}

int main()
{
	NodeList nlist;
	for (int i = 0; i < arrrlens; i++)
		nlist.addToHead(arr[i]);
	//设置6为环的入口节点
	nlist.addLoop(6);
	nlist.printList();
	int is = nlist.isExistLoop();
	printf("%d \n", is);
	int len = nlist.LoopLength();
	printf("len = %d \n", len);
	nlist.printList();
	nlist.getEntryNodeOfLoop();
}