题目17 合并两个排序链表

/////////////////////////////////////////////////////////////////////////////////////
// 7. 题目17 合并两个排序链表
//时间复杂度：O(n), 空间复杂度：O(1)

ListNode<int>* MergeSortedLists(ListNode<int>* plhsHead, ListNode<int>* prhsHead)
{
    if (NULL == plhsHead)
    {
        return prhsHead;
    }

    if (NULL == prhsHead)
    {
        return plhsHead;
    }

    ListNode<int>* pMergeHead = NULL;
    if (plhsHead->m_stData < prhsHead->m_stData)
    {
        pMergeHead = plhsHead;
        pMergeHead->m_pNextNode = MergeSortedLists(plhsHead->m_pNextNode, prhsHead);
    }
    else
    {
        pMergeHead = prhsHead;
        pMergeHead->m_pNextNode = MergeSortedLists(plhsHead, prhsHead->m_pNextNode);
    }

    return pMergeHead;
}

// 非递归方法：合并两个有序链表
//时间复杂度：O(n), 时间复杂度(1)
ListNode<int>* MergeSortedLists_1(ListNode<int>* pHead1, ListNode<int>* pHead2)
{
    if (NULL == pHead1)
    {
        return pHead2;
    }

    if (NULL == pHead2)
    {
        return pHead1;
    }

    // 1.新链表头结点
    ListNode<int>* pMergeHead = NULL;
    if (pHead1->m_stData <= pHead2->m_stData)
    {
        pMergeHead = pHead1;
        pHead1 = pHead1->m_pNextNode;
    }
    else
    {
        pMergeHead = pHead2;
        pHead2 = pHead2->m_pNextNode;
    }

    ListNode<int>* pTmpNode = pMergeHead;

    // 2.比较两个链表，较小的节点加入新链表后面
    while (pHead1 && pHead2)
    {
        if (pHead1->m_stData <= pHead2->m_stData)
        {
            pTmpNode = pHead1;
            pHead1 = pHead1->m_pNextNode;
        }
        else
        {
            pTmpNode = pHead2;
            pHead2 = pHead2->m_pNextNode;
        }

        // 不能让新链表中断！！！！
        if (NULL != pTmpNode->m_pNextNode)
        {
            pTmpNode = pTmpNode->m_pNextNode;
        }
    }

    // 3.链接剩余的元素
    if (pHead1 && pTmpNode)
    {
        pTmpNode->m_pNextNode = pHead1;
    }

    if (pHead2 && pTmpNode)
    {
        pTmpNode->m_pNextNode = pHead2;
    }

    return pMergeHead;
}


void MergeSortedListsTestFunc()
{
    cout << "\n\n --------------- MergeSortedListsTestFunc Start -------------->" << endl;

    // 初始化链表1
    int aiArray[] = {1, 2, 3, 4, 5, 6, 7, 8};
    int iLen = sizeof(aiArray) / sizeof(int);
    TRAVERSAL_ARRAY(aiArray, iLen);

    CSingleList<int>* pList = new CSingleList<int>();
    if (!pList)
    {
        return;
    }

    for (int i = 0; i < iLen; i++)
    {
        pList->Insert(aiArray[i]);
    }
    pList->Traversal();

    // 初始化链表2
    int aiArray2[] = {9, 10, 11, 12, 13, 14, 15};
    int iLen2 = sizeof(aiArray2) / sizeof(int);
    TRAVERSAL_ARRAY(aiArray2, iLen2);

    CSingleList<int>* pList2 = new CSingleList<int>();
    if (!pList2)
    {
        SAVE_DELETE(pList);
        return;
    }

    for (int i = 0; i < iLen2; i++)
    {
        pList2->Insert(aiArray2[i]);
    }

    pList2->Traversal();

    ListNode<int>* pHead1 = pList->GetHeadNode();
    ListNode<int>* pHead2 = pList2->GetHeadNode();

    // 合并链表
    //ListNode<int>* pMergeNode = MergeSortedLists(pHead1, pHead2);
    //if (pMergeNode)
    //{
    //    cout << "两个有序链表合并后: " << endl;
    //    TraversalList(pMergeNode);
    //}

    //cout << "合并后原来链表值: " << endl;
    //pList->Traversal();
    //pList2->Traversal();
    
    ListNode<int>* pMergeNode = MergeSortedLists_1(pHead1, pHead2);
    if (pMergeNode)
    {
        cout << "两个有序链表合并后: " << endl;
        TraversalList(pMergeNode);
    }

    // 释放内存
    SAVE_DELETE(pList);

    // list 与 pList2 已经合并在一起，不用重复释放pLIst2!!!!
    //SAVE_DELETE(pList2);


    cout << "\n\n --------------- MergeSortedListsTestFunc End -------------->" << endl;

}