输入一个单向链表，输出该链表中倒数第K个结点

    输入一个单向链表，输出该链表中倒数第K个结点，具体实现如下：

#include <iostream>
using namespace std;
struct LinkNode
{
public:
	LinkNode(int value = 0) : nValue(value){ pNext = NULL; }
	~LinkNode() { pNext = NULL; }
	//private:
	friend class LinkList;
	int nValue;
	LinkNode *pNext;
};

//带头结点的链表
class LinkList
{
public:
	LinkList();
	~LinkList();
	void Insert(int nData); //插入元素
	void Delete(int nData); //删除元素
	void Sort();    //排序
	bool IsEmpty(); //判断是否为空
	void Reverse(); //反转
	void Destroy(); //销毁整个链表
	int Length();   //链表长度
	LinkNode* Find(int nData);  //查找元素
	bool IsLoop();  //判断是否为环
	void Print();   //打印链表
	LinkNode *FindByIndex(int n);   //返回链表中第i个元素
	LinkNode *FindLastNum(int n);   //使用两个指针 高效操作
private:
	LinkNode *pHead;
};

LinkList::LinkList()
{
	pHead = new LinkNode();
}
LinkList::~LinkList()
{
	Destroy();
}
//从大到小插入
void LinkList::Insert(int nData)
{
	if (pHead == NULL)
	{
		cout << "链表未创建!" << endl;
		return;
	}
	LinkNode *pCur = pHead;
	while (pCur->pNext != NULL)
	{
		if (pCur->pNext->nValue < nData)
		{
			break;
		}
		pCur = pCur->pNext;
	}
	LinkNode *pTmp = new LinkNode(nData);
	pTmp->pNext = pCur->pNext;
	pCur->pNext = pTmp;
}

void LinkList::Delete(int nData)
{
	if (pHead == NULL)
	{
		cout << "链表未创建!" << endl;
		return;
	}
	if (pHead->pNext == NULL)
	{
		cout << "链表为空!" << endl;
		return;
	}

	LinkNode *pCur = pHead;
	while (pCur->pNext)
	{
		if (pCur->pNext->nValue == nData)
		{
			LinkNode *pDel = pCur->pNext;
			pCur->pNext = pCur->pNext->pNext;

			pDel->pNext = NULL;
			delete (pDel);
		}
		else
		{
			pCur = pCur->pNext;
		}
	}
}

void LinkList::Sort()
{
	if (pHead == NULL)
	{
		cout << "链表未创建!" << endl;
		return;
	}
	if (pHead->pNext == NULL)
	{
		cout << "链表为空!" << endl;
	}

	LinkNode *pCur = pHead->pNext;
	LinkNode *pPre = pHead;

	LinkNode *pNewHead = new LinkNode();
	while (pCur)
	{
		LinkNode *pTmp = pCur;
		pCur = pCur->pNext;

		//将pTmp结点插入到pNewHead指向的新链表中
		LinkNode *p = pNewHead;
		while (p->pNext)
		{
			if (p->pNext->nValue > pTmp->nValue)
			{
				break;
			}
			p = p->pNext;
		}
		pTmp->pNext = p->pNext;
		p->pNext = pTmp;
	}
	delete pHead;
	pHead = pNewHead;
}
bool LinkList::IsEmpty()
{
	if (pHead == NULL)
	{
		cout << "链表未创建!" << endl;
		return false;
	}

	return pHead->pNext == NULL;
}

int LinkList::Length()
{
	if (pHead == NULL)
	{
		cout << "链表未创建!" << endl;
		return 0;
	}
	int nLength = 0;
	LinkNode *pCur = pHead->pNext;
	while (pCur)
	{
		nLength++;
		pCur = pCur->pNext;
	}

	return nLength;
}
void LinkList::Reverse()
{
	if (pHead == NULL)
	{
		cout << "链表未创建!" << endl;
	}
	if (pHead->pNext == NULL)
	{
		cout << "链表为空!" << endl;
	}
	else
	{
		LinkNode *pCur = pHead->pNext->pNext;
		LinkNode *pPre = pHead->pNext;
		LinkNode *pnext = NULL;

		while (pCur)
		{
			pnext = pCur->pNext;
			pCur->pNext = pPre;

			pPre = pCur;
			pCur = pnext;
		}

		pHead->pNext->pNext = NULL;
		pHead->pNext = pPre;
	}
}
void LinkList::Destroy()
{
	if (pHead == NULL)
	{
		cout << "链表未创建!" << endl;
		return;
	}

	while (pHead->pNext)
	{
		LinkNode *pDel = pHead->pNext;
		pHead->pNext = pDel->pNext;
		delete pDel;
	}
	delete pHead;
	pHead = NULL;
}
LinkNode* LinkList::Find(int nData)
{
	if (pHead == NULL)
	{
		cout << "链表未创建!" << endl;
		return NULL;
	}
	if (pHead->pNext == NULL)
	{
		cout << "链表为空!" << endl;
		return NULL;
	}

	LinkNode *pCur = pHead->pNext;
	while (pCur != NULL)
	{
		if (pCur->nValue == nData)
		{
			return pCur;
		}
	}

	return NULL;
}
void LinkList::Print()
{
	if (pHead == NULL)
	{
		cout << "链表未创建!" << endl;
		return;
	}
	if (pHead->pNext == NULL)
	{
		cout << "链表为空!" << endl;
		return;
	}
	else
	{
		LinkNode *pCur = pHead->pNext;
		while (pCur)
		{
			cout << pCur->nValue << " ";
			pCur = pCur->pNext;
		}
		cout << endl;
	}
}
bool LinkList::IsLoop()
{
	if (pHead == NULL)
	{
		cout << "链表未创建!" << endl;
		return false;
	}
	if (pHead->pNext == NULL)
	{
		cout << "链表为空!" << endl;
		return false;
	}

	LinkNode *pFast = pHead->pNext;
	LinkNode *pLow = pHead->pNext;

	while (pFast != NULL && pLow != NULL  && pFast->pNext != NULL)
	{
		pFast = pFast->pNext->pNext;
		pLow = pLow->pNext;
		if (pFast == pLow)
		{
			return true;
		}
	}
	return false;
}

LinkNode* LinkList::FindByIndex(int n)
{
	if (n <= 0 || n > Length())
	{
		return NULL;
	}
	LinkNode *pCur = pHead->pNext;
	for (int i = 1; i < n; i++)
	{
		pCur = pCur->pNext;
	}

	return pCur;
}

LinkNode* LinkList::FindLastNum(int n)  //使用两个指针 高效操作
{
	if (pHead == NULL || pHead->pNext == NULL || n < 0)
	{
		return NULL;
	}
	LinkNode *pCur = pHead->pNext;
	LinkNode *pFirst = pHead->pNext;

	while (n > 0)
	{
		pFirst = pFirst->pNext;
		if (pFirst == NULL)
		{
			return NULL;
		}
		n--;
	}
	while (pFirst->pNext)
	{
		pFirst = pFirst->pNext;
		pCur = pCur->pNext;
	}

	return pCur;
}
int main()
{
	LinkList list;
	list.Insert(12);
	list.Insert(14);
	list.Insert(2);
	list.Insert(122);
	list.Insert(5);
	list.Insert(4);
	list.Insert(7);
	list.Print();
	int k;
	cout << "请输入要查询倒数第几个结点(计数从0开始):";
	cin >> k;
	LinkNode *p = list.FindByIndex(list.Length() - k);
	if (p)
	{
		cout << p->nValue << endl;
	}
	LinkNode *p2 = list.FindLastNum(k);
	if (p2)
	{
		cout << p2->nValue << endl;
	}
	system("pause");
	return 0;
}

运行结果如图1所示：

图1 运行效果