#include <iostream>
#include "list.h"
ListNode* FindKthToTail(ListNode* pListHead, unsigned int k)
{
    if(pListHead == NULL || k == 0)
        return NULL;

    ListNode* pAhead = pListHead;
    ListNode* pBehind = NULL;

    //若以pListHead為頭結(jié)點(diǎn)的鏈表結(jié)點(diǎn)總數(shù)少于k
    //for(unsigned int i = 0; i< k-1; ++i)
    //  pAhead = pAhead->m_pNext;
    //這段代碼越界
    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;
}
// ====================測試代碼====================
// 測試要找的結(jié)點(diǎn)在鏈表中間
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);
}

// 測試要找的結(jié)點(diǎn)是鏈表的尾結(jié)點(diǎn)
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);
}

// 測試要找的結(jié)點(diǎn)是鏈表的頭結(jié)點(diǎn)
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);
}

// 測試空鏈表
void Test4()
{
    printf("=====Test4 starts:=====\n");
    printf("expected result: NULL.\n");
    ListNode* pNode = FindKthToTail(NULL, 100);
    PrintListNode(pNode);
}

// 測試輸入的第二個(gè)參數(shù)大于鏈表的結(jié)點(diǎn)總數(shù)
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);
}

// 測試輸入的第二個(gè)參數(shù)為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 main(void)
{
    Test1();
    Test2();
    Test3();
    Test4();
    Test5();
    Test6();

    return 0;
}

結(jié)果

QQ截圖20160626232528.png

相關(guān)

• 判斷單向鏈表是否形成了環(huán)形結(jié)構(gòu)
  定義兩個(gè)指針同時(shí)從鏈表頭結(jié)點(diǎn)出發(fā)，一個(gè)指針一次走一步，另一個(gè)一次走二步。如果走得快的指針追上了走得慢的指針，那么鏈表就是環(huán)形結(jié)構(gòu)；如果走得快的指針走到了鏈表的末尾（m_pNext指向NULL)都沒有追上第一個(gè)指針，那么鏈表就不是環(huán)形結(jié)構(gòu)。

• 求鏈表中間結(jié)點(diǎn)
  如果鏈表中結(jié)點(diǎn)的個(gè)數(shù)是奇數(shù)，返回中間結(jié)點(diǎn)；如果個(gè)數(shù)是偶數(shù)，返回中間結(jié)點(diǎn)中的任何一個(gè)。
  定義兩個(gè)指針同時(shí)從鏈表頭結(jié)點(diǎn)出發(fā)，一個(gè)指針一次走一步，另一個(gè)一次走二步。當(dāng)走得快的指針走到了鏈表的末尾，走得慢的 指針剛好在鏈表中間。

小結(jié)

當(dāng)我們用一個(gè)指針遍歷鏈表不能解決問題的時(shí)候，可以嘗試使用兩個(gè)指針來遍歷。