面试题15之链表中倒数第K个结点_KthNodeFromEnd.cpp

// KthNodeFromEnd.cpp : Defines the entry point for the console application.
//

// 《剑指Offer——名企面试官精讲典型编程题》代码
// 著作权所有者：何海涛

#include "stdafx.h"
#include "Utilities\List.h"

ListNode* FindKthToTail(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;
}

// ====================测试代码====================
// 测试要找的结点在链表中间
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 = FindKthToTail(pNode1, 2);
    PrintListNode(pNode);

    DestroyList(pNode1);
}

// 测试要找的结点是链表的尾结点
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 = FindKthToTail(pNode1, 1);
    PrintListNode(pNode);

    DestroyList(pNode1);
}

// 测试要找的结点是链表的头结点
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 = FindKthToTail(pNode1, 5);
    PrintListNode(pNode);

    DestroyList(pNode1);
}

// 测试空链表
void Test4()
{
    printf("=====Test4 starts:=====\n");
    printf("expected result: NULL.\n");
    ListNode* pNode = FindKthToTail(NULL, 100);
    PrintListNode(pNode);
}

// 测试输入的第二个参数大于链表的结点总数
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 = FindKthToTail(pNode1, 6);
    PrintListNode(pNode);

    DestroyList(pNode1);
}

// 测试输入的第二个参数为0
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 = FindKthToTail(pNode1, 0);
    PrintListNode(pNode);

    DestroyList(pNode1);
}

int _tmain(int argc, _TCHAR* argv[])
{
    Test1();
    Test2();
    Test3();
    Test4();
    Test5();
    Test6();

    return 0;
}