两个链表的第一个公共结点

struct ListNode
{
    int m_nKey;
    ListNode *m_pNext;
};

ListNode *FindFirstCommonNode(ListNode *pHead1, ListNode *pHead2)
{
	//得到两个链表的长度
	unsigned int nLength1 = GetListLength(pHead1);
	unsigned int nLength2 = GetListLength(pHead2);
	int nLengthDif = nLength1 - nLength2;

	ListNode *pListHeadLong = pHead1;
	ListNode *pListHeadShort = pHead2;
	if(nLength2 > nLength1)
	{
		pListHeadLong = pHead2;
		pListHeadShort = pHead1;
		nLengthDif = nLength2 - nLength1;
	}
	
	//先在长链表上走几步，再同时在两个链表上遍历
	for(int i = 0; i < nLengthDif; ++i)
	{
		pListHeadLong = pListHeadLong->m_pNext;
	}

	while((pListHeadLong != NULL) && (pListHeadShort != NULL) && (pListHeadLong != pListHeadShort))
	{
		pListHeadLong = pListHeadLong->m_pNext;
		pListHeadShort = pListHeadShort->m_pNext;
	}

	//得到第一个公共结点
	ListNode *pFirstCommonNode = pListHeadLong;

	return pFirstCommonNode;
}

unsigned int GetListLength(ListNode *pHead)
{
	unsigned int nLength = 0;
	ListNode *pNode = pHead;
	while(pNode != NULL)
	{
		++nLength;
		pNode = pNode->m_pNext;
	}

	return nLength;
}