面试题6：从尾到头打印链表

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。

C++版本

#include<iostream>
#include <stack>


struct ListNode
{
    int       m_nValue;
    ListNode* m_pNext;
};

ListNode* CreateListNode(int value)
{
    ListNode* pNode = new ListNode();
    pNode->m_nValue = value;
    pNode->m_pNext = nullptr;

    return pNode;
}

void ConnectListNodes(ListNode* pCurrent, ListNode* pNext)
{
    if(pCurrent == nullptr)
    {
        printf("Error to connect two nodes.\n");
        exit(1);
    }

    pCurrent->m_pNext = pNext;
}

void PrintListNode(ListNode* pNode)
{
    if(pNode == nullptr)
    {
        printf("The node is nullptr\n");
    }
    else
    {
        printf("The key in node is %d.\n", pNode->m_nValue);
    }
}

void PrintList(ListNode* pHead)
{
    printf("PrintList starts.\n");

    ListNode* pNode = pHead;
    while(pNode != nullptr)
    {
        printf("%d\t", pNode->m_nValue);
        pNode = pNode->m_pNext;
    }

    printf("\nPrintList ends.\n");
}

void DestroyList(ListNode* pHead)
{
    ListNode* pNode = pHead;
    while(pNode != nullptr)
    {
        pHead = pHead->m_pNext;
        delete pNode;
        pNode = pHead;
    }
}

void AddToTail(ListNode** pHead, int value)
{
    ListNode* pNew = new ListNode();
    pNew->m_nValue = value;
    pNew->m_pNext = nullptr;

    if(*pHead == nullptr)
    {
        *pHead = pNew;
    }
    else
    {
        ListNode* pNode = *pHead;
        while(pNode->m_pNext != nullptr)
            pNode = pNode->m_pNext;

        pNode->m_pNext = pNew;
    }
}

void RemoveNode(ListNode** pHead, int value)
{
    if(pHead == nullptr || *pHead == nullptr)
        return;

    ListNode* pToBeDeleted = nullptr;
    if((*pHead)->m_nValue == value)
    {
        pToBeDeleted = *pHead;
        *pHead = (*pHead)->m_pNext;
    }
    else
    {
        ListNode* pNode = *pHead;
        while(pNode->m_pNext != nullptr && pNode->m_pNext->m_nValue != value)
            pNode = pNode->m_pNext;

        if(pNode->m_pNext != nullptr && pNode->m_pNext->m_nValue == value)
        {
            pToBeDeleted = pNode->m_pNext;
            pNode->m_pNext = pNode->m_pNext->m_pNext;
        }
    }

    if(pToBeDeleted != nullptr)
    {
        delete pToBeDeleted;
        pToBeDeleted = nullptr;
    }
}

void PrintListReversingly_Iteratively(ListNode* pHead)
{
    std::stack<ListNode*> 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_nValue);
        nodes.pop();
    }
}

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

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

// ====================测试代码====================
void Test(ListNode* pHead)
{
    PrintList(pHead);
    PrintListReversingly_Iteratively(pHead);
    printf("\n");
    PrintListReversingly_Recursively(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();

    return 0;
}

Java版本

public static ArrayList<Integer> printListFromTailToHead(ListNode listNode) {
        ArrayList<Integer> arrayList = new ArrayList<Integer>();
        
        // 用栈来储存
        Stack<ListNode> stack = new Stack<ListNode>();
        while(listNode != null) {
        	stack.push(listNode);
        	listNode = listNode.next;
        }
        
        // 放回链表
        while(!stack.empty()) {
        	ListNode lNode = stack.peek();
        	arrayList.add(lNode.val);
        	stack.pop();
        }
        return arrayList;
    }