《剑指offer》面试题06：从尾到头打印链表

更多剑指offer面试习题请点击：《剑指offer》（第二版）题集目录索引

题目：
　　输入一个链表的头结点，从尾到头反过来打印出每个结点的值。

解题思路：
　　关于这题我们可以用三种方法解决：
　　1. 栈
　　2. 递归
　　3. 循环

< code1_stack>

void PrintListReversingly_Iteratively(ListNode* pHead)
{
    std::stack nodes;

    ListNode* pNode = pHead;
    while (pNode != nullptr)
    {
        nodes.push(pNode);
        pNode = pNode->m_pNext;
    }

    while (!nodes.empty())
    {
        pNode = nodes.top();
        printf("%d\t", pNode->m_nKey);
        nodes.pop();
    }
}

< code2_Recursively >

void PrintListReversingly_Recursively(ListNode* pHead)
{
    if (pHead != nullptr)
    {
        if (pHead->m_pNext != nullptr)
        {
            PrintListReversingly_Recursively(pHead->m_pNext);
        }

        printf("%d\t", pHead->m_nKey);
    }
}

< code3_Loop >

void PrintListReversingly_Loop(ListNode* pHead)
{
    if (pHead != nullptr)
    {
        ListNode* cur = pHead;
        ListNode* tail = nullptr;

        while (tail != pHead)
        {
            cur = pHead;
            while (cur->m_pNext != tail)
            {
                cur = cur->m_pNext;
            }
            printf("%d\t", cur->m_nKey);
            tail = cur;
        }
    }
}

< Test code>

void PrintList(ListNode* pNode)
{
    if (pNode != nullptr)
    {
        printf("%d", pNode->m_nKey);
    }
}

ListNode* CreateListNode(int value)
{
    ListNode* tmp = new ListNode;
    tmp->m_nKey = value;
    tmp->m_pNext = nullptr;

    return tmp;
}

void ConnectListNodes(ListNode* pNode1, ListNode* pNode2)
{
    if (pNode1 != nullptr)
    {
        pNode1->m_pNext = pNode2;
    }
}

void DestroyList(ListNode* pHead)
{
    ListNode* pNext = nullptr; 

    while (pHead != nullptr)
    {
        pNext = pHead->m_pNext;
        delete pHead;
        pHead = pNext;
    }
    pHead = nullptr;
}







void Test(ListNode* pHead)
{
    //PrintList(pHead);
    PrintListReversingly_Iteratively(pHead);
    printf("\n");
    PrintListReversingly_Recursively(pHead);
    printf("\n");
    PrintListReversingly_Loop(pHead);
}

// 1->2->3->4->5
void Test1()
{
    printf("\nTest1 begins.\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);

    Test(pNode1);

    DestroyList(pNode1);
}

// 只有一个结点的链表: 1
void Test2()
{
    printf("\nTest2 begins.\n");

    ListNode* pNode1 = CreateListNode(1);

    Test(pNode1);

    DestroyList(pNode1);
}

// 空链表
void Test3()
{
    printf("\nTest3 begins.\n");

    Test(nullptr);
}

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

    system("pause");
    return 0;
}

测试结果：