剑指offer——面试题22：链表中倒数第k个节点

注意代码的鲁棒性！

函数：

ListNode* TheLastKthNode(ListNode* pHead,int k)
{
    if(pHead==nullptr || k<=0)
        return nullptr;
    ListNode* quickNode=pHead;
    ListNode* slowNode=pHead;
    int cnt=1;
    while(quickNode->m_pNext!=nullptr&&cnt<k)
    {
        quickNode=quickNode->m_pNext;
        ++cnt;
    }
    if(cnt<k)
        return nullptr;
    while(quickNode->m_pNext!=nullptr)
    {
        quickNode=quickNode->m_pNext;
        slowNode=slowNode->m_pNext;
    }
    return slowNode;
}

测试代码：

#include"List.h"

void Test(char* testName,ListNode* pHead,int k,int expect)
{
    cout<<testName<<":";
    ListNode* result=TheLastKthNode(pHead,k);
    if(result==nullptr)
    {
        cout<<"Invalid input."<<endl;
    }
    else if(result->m_Value==expect)
    {
        cout<<"Passed."<<endl;
    }
    else
        cout<<"Failed."<<endl;
}

void Test1_7()
{
    ListNode* pNode1=CreateListNode(1);

    Test("test0",pNode1,1,1);
    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);

    Test("test1",pNode1,0,-1);
    Test("test2",pNode1,1,5);
    Test("test3",pNode1,2,4);
    Test("test4",pNode1,3,3);
    Test("test5",pNode1,4,2);
    Test("test6",pNode1,5,1);

    Test("test7",nullptr,5,-1);

}

int main()
{
    Test1_7();
    return 0;
}