剑指offer

// 面试题23：链表中环的入口结点
// 题目：一个链表中包含环，如何找出环的入口结点？例如，在图3.8的链表中，
// 环的入口结点是结点3。

ListNode* FindFirstNode(ListNode* HeadNode)
{
    if(!HeadNode)
        return nullptr;
    ListNode* FastNode = HeadNode;
    ListNode* SlowNode = HeadNode;
    while(FastNode&(FastNode->NextPoint))
    {
        SlowNode = SlowNode->NextPoint;
        FastNode = SlowNode->NextPoint;
        if(FastNode == SlowNode)
        {
            SlowNode = HeadNode;
            while(FastNode != SlowNode)
            {
                FastNode = FastNode->NextPoint;
                SlowNode = SlowNode->NextPoint;
            }
            return SlowNode;
        }
    }
    return nullptr;
}

//找到链表中环形链表的入口点
ListNode* FindTheFirstNode(ListNode* Node)
{
    if(Node ==nullptr)
        return nullptr;
    ListNode* Fastp = Node;
    ListNode  Slowp = Node;
    while((Fastp!= Slowp)&(Fastp!=nullptr))
    {
        Fastp = Fastp->NextPoint->NextPoint;
        Slowp = Slowp->NextPoint;
    }
    Slowp =Node;
    while(SLowp != Fastp)
    {
        Slowp = Slowp->NextPoint;
        Fastp = Fastp->NextPoint;
    }
    return slowp;
}

　　// 面试题22：链表中倒数第k个结点
// 题目：输入一个链表，输出该链表中倒数第k个结点。为了符合大多数人的习惯，
// 本题从1开始计数，即链表的尾结点是倒数第1个结点。例如一个链表有6个结点，
// 从头结点开始它们的值依次是1、2、3、4、5、6。这个链表的倒数第3个结点是
// 值为4的结点。

#include <cstdio>
#include "..\Utilities\List.h"

ListNode* FindKthToTail(ListNode* pListHead, unsigned int k)
{
    if(pListHead == nullptr || k == 0)
        return nullptr;

    ListNode *pAhead = pListHead;
    ListNode *pBehind = nullptr;

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

    pBehind = pListHead;
    while(pAhead->m_pNext != nullptr)
    {
        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: nullptr.\n");
    ListNode* pNode = FindKthToTail(nullptr, 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: nullptr.\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: nullptr.\n");
    ListNode* pNode = FindKthToTail(pNode1, 0);
    PrintListNode(pNode);

    DestroyList(pNode1);
}

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

    return 0;
}

 

标签：结点,ListNode,CreateListNode,offer,pNode1,ConnectListNodes,链表
来源： https://www.cnblogs.com/hai5111/p/11423633.html