算法题目---链表中倒数第k个结点

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输入一个链表，输出该链表中倒数第k个结点。

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

ListNode* CreateListNode(int value)
{
    ListNode* pNode = new ListNode();
    pNode->m_nValue = value;
    pNode->m_pNext = NULL;

    return pNode;
}

void ConnectListNodes(ListNode* pCurrent, ListNode* pNext)
{
    if(pCurrent == NULL)
    {
        printf("Error to connect two nodes.\n");
    }

    pCurrent->m_pNext = pNext;
}

void PrintListNode(ListNode* pNode)
{
    if(pNode == NULL)
    {
        printf("The node is NULL\n");
    }
    else
    {
        printf("The key in node is %d.\n", pNode->m_nValue);
    }
}

ListNode *FindKth(ListNode *pListHead,unsigned int k)
{
   if(pListHead == NULL || k == 0)
       return NULL;
   ListNode *pAhead = pListHead;
   ListNode *pBehind = NULL;

   for(unsigned int i=0;i<k-1;++i)
   {
       if(pAhead->m_pNext != NULL)
           pAhead = pAhead->m_pNext;
       else
       {
           return NULL;
       }
   }

   pBehind = pListHead;
   while(pAhead->m_pNext != NULL)
   {
       pAhead = pAhead->m_pNext;
       pBehind = pBehind->m_pNext;
   }
   return pBehind;
}

void DestroyList(ListNode* pHead)
{
    ListNode* pNode = pHead;
    while(pNode != NULL)
    {
        pHead = pHead->m_pNext;
        delete pNode;
        pNode = pHead;
    }
}

void Test1()
{
    printf("=====Test1 starts:=====\n");
    ListNode* pNode1 = CreateListNode(1);
    ListNode* pNode2 = CreateListNode(2);
    ListNode* pNode3 = CreateListNode(3);
    ListNode* pNode4 = CreateListNode(4);
    ListNode* pNode5 = CreateListNode(5);

    ConnectListNodes(pNode1, pNode2);
    ConnectListNodes(pNode2, pNode3);
    ConnectListNodes(pNode3, pNode4);
    ConnectListNodes(pNode4, pNode5);

    printf("expected result: 4.\n");
    ListNode* pNode = FindKth(pNode1, 2);
    PrintListNode(pNode);

    DestroyList(pNode1);
}

void Test2()
{
    printf("=====Test2 starts:=====\n");
    ListNode* pNode1 = CreateListNode(1);
    ListNode* pNode2 = CreateListNode(2);
    ListNode* pNode3 = CreateListNode(3);
    ListNode* pNode4 = CreateListNode(4);
    ListNode* pNode5 = CreateListNode(5);

    ConnectListNodes(pNode1, pNode2);
    ConnectListNodes(pNode2, pNode3);
    ConnectListNodes(pNode3, pNode4);
    ConnectListNodes(pNode4, pNode5);

    printf("expected result: 5.\n");
    ListNode* pNode = FindKth(pNode1, 1);
    PrintListNode(pNode);

    DestroyList(pNode1);
}

void Test3()
{
    printf("=====Test3 starts:=====\n");
    ListNode* pNode1 = CreateListNode(1);
    ListNode* pNode2 = CreateListNode(2);
    ListNode* pNode3 = CreateListNode(3);
    ListNode* pNode4 = CreateListNode(4);
    ListNode* pNode5 = CreateListNode(5);

    ConnectListNodes(pNode1, pNode2);
    ConnectListNodes(pNode2, pNode3);
    ConnectListNodes(pNode3, pNode4);
    ConnectListNodes(pNode4, pNode5);

    printf("expected result: 1.\n");
    ListNode* pNode = FindKth(pNode1, 5);
    PrintListNode(pNode);

    DestroyList(pNode1);
}

void Test4()
{
    printf("=====Test4 starts:=====\n");
    printf("expected result: NULL.\n");
    ListNode* pNode = FindKth(NULL, 100);
    PrintListNode(pNode);
}

void Test5()
{
    printf("=====Test5 starts:=====\n");
    ListNode* pNode1 = CreateListNode(1);
    ListNode* pNode2 = CreateListNode(2);
    ListNode* pNode3 = CreateListNode(3);
    ListNode* pNode4 = CreateListNode(4);
    ListNode* pNode5 = CreateListNode(5);

    ConnectListNodes(pNode1, pNode2);
    ConnectListNodes(pNode2, pNode3);
    ConnectListNodes(pNode3, pNode4);
    ConnectListNodes(pNode4, pNode5);

    printf("expected result: NULL.\n");
    ListNode* pNode = FindKth(pNode1, 6);
    PrintListNode(pNode);

    DestroyList(pNode1);
}

void Test6()
{
    printf("=====Test6 starts:=====\n");
    ListNode* pNode1 = CreateListNode(1);
    ListNode* pNode2 = CreateListNode(2);
    ListNode* pNode3 = CreateListNode(3);
    ListNode* pNode4 = CreateListNode(4);
    ListNode* pNode5 = CreateListNode(5);

    ConnectListNodes(pNode1, pNode2);
    ConnectListNodes(pNode2, pNode3);
    ConnectListNodes(pNode3, pNode4);
    ConnectListNodes(pNode4, pNode5);

    printf("expected result: NULL.\n");
    ListNode* pNode = FindKth(pNode1, 0);
    PrintListNode(pNode);

    DestroyList(pNode1);
}

int main()
{
    Test1();
    Test2();
    Test3();
    Test4();
    Test5();
    Test6();
   return 0;
}

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