1.合并两个有序的链表

一、题目

　　合并两个有序的链表并使新链表也是有序排列。

二、算法实现

ListNode* Merge(ListNode* pHead1, ListNode* pHead2)
{
    if (pHead1 == NULL)
        return pHead2;
    else if (pHead2 == NULL)
        return pHead1;
    ListNode *pNewHead = NULL, *pNode1 = NULL, *pNode2 = NULL;
    if (pHead1->m_nValue <= pHead2->m_nValue)
    {
        pNewHead = pHead1;
        pNode1 = pHead1->m_pNext;
        pNode2 = pHead2;
    } 
    else
    {
        pNewHead = pHead2;
        pNode1 = pHead1;
        pNode2 = pHead2->m_pNext;
    }

    ListNode* pNewListLastNode = pNewHead;

    while (pNode1 != NULL && pNode2 != NULL)
    {
        if (pNode1->m_nValue <= pNode2->m_nValue)
        {
            pNewListLastNode->m_pNext = pNode1;
            pNewListLastNode = pNode1;
            pNode1 = pNode1->m_pNext;
        } 
        else
        {
            pNewListLastNode->m_pNext = pNode2;
            pNewListLastNode = pNode2;
            pNode2 = pNode2->m_pNext;
        }
    }

    // 一个链表遍历完了，另一个直接链接到后面即可
    if (pNode1 == NULL)
    {
        pNewListLastNode->m_pNext = pNode2;
    }
    else
    {
        pNewListLastNode->m_pNext = pNode1;
    }

    return pNewHead;
}