C++算法之 查找链表中间节点

解析：设立两个指针，p每次移动两下，q每次只移动一下，那么当p指向最后一个节点的时候，那么q就是中间的节点了

ListNode* FindMidNode(ListNode* pHead)
{
	if (pHead == NULL)
	{
		return NULL;
	}
	if (pHead->m_pNext == NULL || pHead->m_pNext->m_pNext == NULL)
	{
		return pHead;
	}
	ListNode* pFirstNode  = pHead;
	ListNode* pSecondNode = pHead;

	while(pFirstNode->m_pNext!= NULL && pFirstNode->m_pNext->m_pNext != NULL)//如果链表结点数为偶数，输出中间两个结点前面的一个。
	{
		pFirstNode  = pFirstNode->m_pNext->m_pNext;
		pSecondNode = pSecondNode->m_pNext;
	}

	return pSecondNode;
}

// FindMidNodeList.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <iostream>
using namespace std;

struct ListNode
{
	int  m_nValue;
	ListNode* m_pNext;
	ListNode(int k): m_nValue(k),m_pNext(NULL)
	{

	}
};

ListNode* FindMidNode(ListNode* pHead)
{
	if (pHead == NULL)
	{
		return NULL;
	}
	if (pHead->m_pNext == NULL || pHead->m_pNext->m_pNext == NULL)
	{
		return pHead;
	}
	ListNode* pFirstNode  = pHead;
	ListNode* pSecondNode = pHead;

	while(pFirstNode->m_pNext!= NULL && pFirstNode->m_pNext->m_pNext != NULL)//如果链表结点数为偶数，输出中间两个结点前面的一个。
	{
		pFirstNode  = pFirstNode->m_pNext->m_pNext;
		pSecondNode = pSecondNode->m_pNext;
	}

	return pSecondNode;
}

int _tmain(int argc, _TCHAR* argv[])
{

	ListNode* head  = new ListNode(1);
	ListNode* Node1 = new ListNode(2);
	ListNode* Node2 = new ListNode(3);
	ListNode* Node3 = new ListNode(4);
	ListNode* Node4 = new ListNode(5);
	ListNode* Node5 = new ListNode(6);
	ListNode* Node6 = new ListNode(7);

	head->m_pNext = Node1;
	Node1->m_pNext = Node2;
	Node2->m_pNext = Node3;
	Node3->m_pNext = Node4;
	Node4->m_pNext = Node5;
	Node5->m_pNext = NULL;
	//Node6->m_pNext = NULL;

	ListNode* p = FindMidNode(head);
	cout<<p->m_nValue<<endl;

	getchar();
	return 0;
}