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  • 从尾到头打印链表(C++和Python 实现)

    (说明:本博客中的题目题目详细说明参考代码均摘自 “何海涛《剑指Offer:名企面试官精讲典型编程题》2012年”)

    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。

    进一步详细说明:
    不允许在打印时修改链表的结构。链表结点可定义为:

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

    算法设计思想

    正常情况,遍历链表都是从前到后的,即从头到尾。如果从尾到头打印链表元素,可以借助栈的 “后入先出” (Last in, First out)的性质,在正向遍历时将链表元素依次压栈,当到达链表末尾时,再依次弹出并打印。

    具体实现可以采用两种方法:迭代和递归。正如书中所说,“递归在本质上就是一个栈结构”。递归实现,从理论上,完全可以利用栈结构转换为非递归实现,即迭代方法。

    C++ 实现

    #include <iostream>
    #include <stack>
    
    struct ListNode
    {
        int  m_nKey;
        ListNode* m_pNext;
    };
    
    void AddToTail(ListNode** pHead, int value)
    {
        ListNode* pNew = new ListNode();
        pNew->m_nKey = value;
        pNew->m_pNext = NULL;
    
        if (*pHead == NULL)
        {
            *pHead = pNew;
        }
        else
        {
            ListNode* pNode = *pHead;
            while (pNode->m_pNext != NULL)
                pNode = pNode->m_pNext;
            pNode->m_pNext = pNew;
        }
    }
    
    
    void PrintLinkedList(const ListNode* head)
    {
        if (head == NULL)  // 易漏点
            return;
    
        ListNode* ptr = (ListNode*) head;
        while (ptr->m_pNext != NULL)
        {
            std::cout << ptr->m_nKey << " -> ";
            ptr = ptr->m_pNext;
        }
    
        std::cout << ptr->m_nKey << std::endl;
    }
    
    void DestroyLinkedList(ListNode** pHead)
    {
        if (pHead == NULL || *pHead == NULL)  // 易漏点
            return;
    
        ListNode* pNode = NULL;
        while (*pHead != NULL)
        {
            pNode = *pHead;
            *pHead = (*pHead)->m_pNext;
            delete pNode;
        }
    }
    
    // Iterative method
    void PrintListReversingly_Iteratively(const ListNode* pHead)
    {
        if (pHead == NULL)
            return;
    
        ListNode* pNode = (ListNode*) pHead;
        std::stack<ListNode*> nodes;
    
        while (pNode != NULL)
        {
            nodes.push(pNode);
            pNode = pNode->m_pNext;
        }
    
        while (!nodes.empty())
        {
            pNode = nodes.top();
            nodes.pop();
            std::cout << pNode->m_nKey << ", ";
        }
        std::cout << std::endl;
    }
    
    // Recursive method
    void PrintListReversingly_Recursively(const ListNode* pHead)
    {
        if (pHead != NULL)
        {
            if (pHead->m_pNext != NULL)
            {
                PrintListReversingly_Recursively(pHead->m_pNext);
            }
    
            std::cout << pHead->m_nKey << ", ";
        }
    }
    
    void unitest()
    {
        ListNode* head = NULL;
    
        AddToTail(&head, 1);
        AddToTail(&head, 2);
        AddToTail(&head, 3);
        AddToTail(&head, 5);
        AddToTail(&head, 4);
    
        std::cout << "Print forward: ";
        PrintLinkedList(head);
        std::cout << "Print reversely iteratively: ";
        PrintListReversingly_Iteratively(head);
        std::cout << "Print reversely recursively: ";
        PrintListReversingly_Recursively(head);
    
        // Release memory
        DestroyLinkedList(&head);   // 易漏点
    }
    
    int main()
    {
        unitest();
    
        return 0;
    }

     

    Python 实现

    #!/usr/bin/python
    # -*- coding: utf8 -*-
    
    from __future__ import print_function
    
    
    class ListNode:
        def __init__(self, value, next_node=None):
            self.value = value
            self.next = next_node
    
    
    def add_to_tail(head, value):
        q = ListNode(value)
    
        if head is None:
            head = q
        else:
            p = head
            while p.next is not None:
                p = p.next
            p.next = q
    
        return head 
    
    
    def print_list_reversely_iteratively(head):
        p = head
        stack = []
        # Push into stack
        while p is not None:
            stack.append(p.value)
            p = p.next
        # Pop from stack
        while stack:
            elem = stack.pop()
            print(elem, end=', ')
        print('')
    
        
    def print_list_reversely_recursively(head):
        if head is None:
            return
        if head.next is not None:
            print_list_reversely_recursively(head.next)
        print(head.value, end=', ')
            
    
    def print_linked_list_forward(head):
        if head is None:
            print("This linked list is empty!")
            return
        
        p = head
        while p is not None:
            print(p.value, end='')
            if p.next is not None:
                print(' -> ', end='')
            p = p.next
        print('')
    
                
    def unitest():
        linked_list = None
        linked_list = add_to_tail(linked_list, 1)
        linked_list = add_to_tail(linked_list, 2)
        linked_list = add_to_tail(linked_list, 3)
        linked_list = add_to_tail(linked_list, 5)
        linked_list = add_to_tail(linked_list, 4)
        print("Print forward: ", end='')
        print_linked_list_forward(linked_list)
        print("Print reversely iteratively: ", end='') 
        print_list_reversely_iteratively(linked_list)
        print("Print reversely recursively: ", end='') 
        print_list_reversely_recursively(linked_list)
    
    
    if __name__ == '__main__':
        unitest()

    注:使用 Python 利用函数建立链表时,需要注意函数参数的值传递和引用传递,此为易错点

    参考代码

    1. targetver.h (05_PrintListInReversedOrder/ 目录)

    #pragma once
    
    // The following macros define the minimum required platform.  The minimum required platform
    // is the earliest version of Windows, Internet Explorer etc. that has the necessary features to run 
    // your application.  The macros work by enabling all features available on platform versions up to and 
    // including the version specified.
    
    // Modify the following defines if you have to target a platform prior to the ones specified below.
    // Refer to MSDN for the latest info on corresponding values for different platforms.
    #ifndef _WIN32_WINNT            // Specifies that the minimum required platform is Windows Vista.
    #define _WIN32_WINNT 0x0600     // Change this to the appropriate value to target other versions of Windows.
    #endif
    View Code

    2. stdafx.h (05_PrintListInReversedOrder/ 目录)

    // stdafx.h : include file for standard system include files,
    // or project specific include files that are used frequently, but
    // are changed infrequently
    //
    
    #pragma once
    
    #include "targetver.h"
    
    #include <stdio.h>
    #include <tchar.h>
    
    
    
    // TODO: reference additional headers your program requires here
    View Code

    3. stdafx.cpp (05_PrintListInReversedOrder/ 目录)

    // stdafx.cpp : source file that includes just the standard includes
    // PrintListInReversedOrder.pch will be the pre-compiled header
    // stdafx.obj will contain the pre-compiled type information
    
    #include "stdafx.h"
    
    // TODO: reference any additional headers you need in STDAFX.H
    // and not in this file
    View Code

    4. PrintListInReversedOrder.cpp

    // PrintListInReversedOrder.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 "..UtilitiesList.h"
    #include <stack>
    
    void PrintListReversingly_Iteratively(ListNode* pHead)
    {
        std::stack<ListNode*> nodes;
    
        ListNode* pNode = pHead;
        while(pNode != NULL)
        {
            nodes.push(pNode);
            pNode = pNode->m_pNext;
        }
    
        while(!nodes.empty())
        {
            pNode = nodes.top();
            printf("%d	", pNode->m_nValue);
            nodes.pop();
        }
    }
    
    void PrintListReversingly_Recursively(ListNode* pHead)
    {
        if(pHead != NULL)
        {
            if (pHead->m_pNext != NULL)
            {
                PrintListReversingly_Recursively(pHead->m_pNext);
            }
     
            printf("%d	", pHead->m_nValue);
        }
    }
    
    void Test(ListNode* pHead)
    {
        PrintList(pHead);
        PrintListReversingly_Iteratively(pHead);
        printf("
    ");
        PrintListReversingly_Recursively(pHead);
    }
    
    // 1->2->3->4->5
    void Test1()
    {
        printf("
    Test1 begins.
    ");
    
        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("
    Test2 begins.
    ");
    
        ListNode* pNode1 = CreateListNode(1);
    
        Test(pNode1);
    
        DestroyList(pNode1);
    }
    
    // 空链表
    void Test3()
    {
        printf("
    Test3 begins.
    ");
    
        Test(NULL);
    }
    
    int _tmain(int argc, _TCHAR* argv[])
    {
        Test1();
        Test2();
        Test3();
    
        return 0;
    }
    View Code

    5. targetver.h (Utilities/ 目录)

    #pragma once
    
    // The following macros define the minimum required platform.  The minimum required platform
    // is the earliest version of Windows, Internet Explorer etc. that has the necessary features to run 
    // your application.  The macros work by enabling all features available on platform versions up to and 
    // including the version specified.
    
    // Modify the following defines if you have to target a platform prior to the ones specified below.
    // Refer to MSDN for the latest info on corresponding values for different platforms.
    #ifndef WINVER                          // Specifies that the minimum required platform is Windows Vista.
    #define WINVER 0x0600           // Change this to the appropriate value to target other versions of Windows.
    #endif
    
    #ifndef _WIN32_WINNT            // Specifies that the minimum required platform is Windows Vista.
    #define _WIN32_WINNT 0x0600     // Change this to the appropriate value to target other versions of Windows.
    #endif
    
    #ifndef _WIN32_WINDOWS          // Specifies that the minimum required platform is Windows 98.
    #define _WIN32_WINDOWS 0x0410 // Change this to the appropriate value to target Windows Me or later.
    #endif
    
    #ifndef _WIN32_IE                       // Specifies that the minimum required platform is Internet Explorer 7.0.
    #define _WIN32_IE 0x0700        // Change this to the appropriate value to target other versions of IE.
    #endif
    View Code

    6. stdafx.h (Utilities/ 目录)

    // stdafx.h : include file for standard system include files,
    // or project specific include files that are used frequently, but
    // are changed infrequently
    //
    
    #pragma once
    
    #include "targetver.h"
    
    #define WIN32_LEAN_AND_MEAN             // Exclude rarely-used stuff from Windows headers
    // Windows Header Files:
    #include <windows.h>
    #include <stdio.h>
    
    
    // TODO: reference additional headers your program requires here
    View Code

    7. stdafx.cpp (Utilities/ 目录)

    // stdafx.cpp : source file that includes just the standard includes
    // Utilities.pch will be the pre-compiled header
    // stdafx.obj will contain the pre-compiled type information
    
    #include "stdafx.h"
    
    // TODO: reference any additional headers you need in STDAFX.H
    // and not in this file
    View Code

    8. List.h 

    // 《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
    
    struct ListNode
    {
        int       m_nValue;
        ListNode* m_pNext;
    };
    
    __declspec( dllexport ) ListNode* CreateListNode(int value);
    __declspec( dllexport ) void ConnectListNodes(ListNode* pCurrent, ListNode* pNext);
    __declspec( dllexport ) void PrintListNode(ListNode* pNode);
    __declspec( dllexport ) void PrintList(ListNode* pHead);
    __declspec( dllexport ) void DestroyList(ListNode* pHead);
    __declspec( dllexport ) void AddToTail(ListNode** pHead, int value);
    __declspec( dllexport ) void RemoveNode(ListNode** pHead, int value);
    View Code

    9. List.cpp 

    // Utilities.cpp : Defines the exported functions for the DLL 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 "list.h"
    #include <stdio.h>
    #include <stdlib.h>
    
    ListNode* CreateListNode(int value)
    {
        ListNode* pNode = new ListNode();
        pNode->m_nValue = value;
        pNode->m_pNext = NULL;
    
        return pNode;
    }
    
    void ConnectListNodes(ListNode* pCurrent, ListNode* pNext)
    {
        if(pCurrent == NULL)
        {
            printf("Error to connect two nodes.
    ");
            exit(1);
        }
    
        pCurrent->m_pNext = pNext;
    }
    
    void PrintListNode(ListNode* pNode)
    { 
        if(pNode == NULL)
        {
            printf("The node is NULL
    ");
        }
        else
        {
            printf("The key in node is %d.
    ", pNode->m_nValue);
        }
    }
    
    void PrintList(ListNode* pHead)
    {
        printf("PrintList starts.
    ");
        
        ListNode* pNode = pHead;
        while(pNode != NULL)
        {
            printf("%d	", pNode->m_nValue);
            pNode = pNode->m_pNext;
        }
    
        printf("
    PrintList ends.
    ");
    }
    
    void DestroyList(ListNode* pHead)
    {
        ListNode* pNode = pHead;
        while(pNode != NULL)
        {
            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 = NULL;
    
        if(*pHead == NULL)
        {
            *pHead = pNew;
        }
        else
        {
            ListNode* pNode = *pHead;
            while(pNode->m_pNext != NULL)
                pNode = pNode->m_pNext;
    
            pNode->m_pNext = pNew;
        }
    }
    
    void RemoveNode(ListNode** pHead, int value)
    {
        if(pHead == NULL || *pHead == NULL)
            return;
    
        ListNode* pToBeDeleted = NULL;
        if((*pHead)->m_nValue == value)
        {
            pToBeDeleted = *pHead;
            *pHead = (*pHead)->m_pNext;
        }
        else
        {
            ListNode* pNode = *pHead;
            while(pNode->m_pNext != NULL && pNode->m_pNext->m_nValue != value)
                pNode = pNode->m_pNext;
    
            if(pNode->m_pNext != NULL && pNode->m_pNext->m_nValue == value)
            {
                pToBeDeleted = pNode->m_pNext;
                pNode->m_pNext = pNode->m_pNext->m_pNext;
            }
        }
    
        if(pToBeDeleted != NULL)
        {
            delete pToBeDeleted;
            pToBeDeleted = NULL;
        }
    }
    View Code

    10. 参考代码下载

    项目 05_PrintListInReversedOrder 下载: 百度网盘

    何海涛《剑指Offer:名企面试官精讲典型编程题》 所有参考代码下载:百度网盘

    参考资料

    [1]  何海涛. 剑指 Offer:名企面试官精讲典型编程题 [M]. 北京:电子工业出版社,2012. 49-53.

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  • 原文地址:https://www.cnblogs.com/klchang/p/7590302.html
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