不开辟新空间反转单链表(递归版本)

ListNode* ReverseList(ListNode* pHead, ListNode*& pNewHead )
{
if ( NULL == pHead )
return NULL;

ListNode* pPrev = NULL;

if ( NULL != pHead->m_pNext )
pPrev = ReverseList( pHead->m_pNext, pNewHead );
else//注意得保存下新的头
pNewHead = pHead;

if ( NULL != pPrev )//注意递归第一次，pPrev为NULL，所以得加条件判断
pPrev->m_pNext = pHead;

return pHead;
}

#include <iostream>
using namespace std;

struct ListNode{
int m_nKey;
ListNode* m_pNext;

ListNode( ListNode* pNext, int value )
: m_pNext( pNext )
, m_nKey( value )
{}
};

void push_back( ListNode** pHead, int value );
ListNode* Find( ListNode* pListHead, int value );
ListNode* ReverseList(ListNode* pHead, ListNode*& pNewHead );

int main( )
{
ListNode* pHead = NULL;

//push_back( &pHead, 1 );

/*push_back( &pHead, 1 );
push_back( &pHead, 2 );*/

//push_back( &pHead, 1 );
//push_back( &pHead, 2 );
//push_back( &pHead, 3 );
//push_back( &pHead, 4 );

ListNode* pNewHead = NULL;
ReverseList( pHead, pNewHead );

if ( NULL != pHead )						//坑1
pHead->m_pNext = NULL;

while ( NULL != pNewHead ){
//坑2.小心别 NULL != pNewHead  这样会遗漏最后一个结点
cout << pNewHead->m_nKey << " ";
pNewHead = pNewHead->m_pNext;
}

cout << endl;

return 0;
}

void push_back( ListNode** pHead, int value )
{
if ( NULL == pHead )
return;

ListNode* pNewNode = new ListNode( NULL, value );

if ( NULL == *pHead ){
*pHead = pNewNode;
return;
}

ListNode* pNode = *pHead;

while ( NULL != pNode->m_pNext )
pNode = pNode->m_pNext;

pNode->m_pNext = pNewNode;
}

ListNode* Find( ListNode* pListHead, int value )
{
if ( NULL == pListHead )
return NULL;

ListNode* pNode = pListHead;

while ( NULL != pNode && value != pNode->m_nKey )
pNode = pNode->m_pNext;

if ( NULL == pNode )
return NULL;

return pNode;
}

ListNode* ReverseList(ListNode* pHead, ListNode*& pNewHead )
{
if ( NULL == pHead )
return NULL;

ListNode* pPrev = NULL;

if ( NULL != pHead->m_pNext )
pPrev = ReverseList( pHead->m_pNext, pNewHead );
else//注意得保存下新的头
pNewHead = pHead;

if ( NULL != pPrev )//注意递归第一次，pPrev为NULL，所以得加条件判断
pPrev->m_pNext = pHead;

return pHead;
}