从尾到头打印链表（C++和Python 实现）

（说明：本博客中的题目、题目详细说明及参考代码均摘自 “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 memoryDestroyLinkedList(&head);   // 易漏点
}int main()
{unitest();return 0;
}

Python 实现

#!/usr/bin/python
# -*- coding: utf8 -*-from __future__ import print_functionclass ListNode:def __init__(self, value, next_node=None):self.value = valueself.next = next_nodedef add_to_tail(head, value):q = ListNode(value)if head is None:head = qelse:p = headwhile p.next is not None:p = p.nextp.next = qreturn head def print_list_reversely_iteratively(head):p = headstack = []# Push into stackwhile p is not None:stack.append(p.value)p = p.next# Pop from stackwhile stack:elem = stack.pop()print(elem, end=', ')print('')def print_list_reversely_recursively(head):if head is None:returnif 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!")returnp = headwhile p is not None:print(p.value, end='')if p.next is not None:print(' -> ', end='')p = p.nextprint('')def unitest():linked_list = Nonelinked_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

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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

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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

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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 "..\Utilities\List.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\t", 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\t", pHead->m_nValue);}
}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(NULL);
}int _tmain(int argc, _TCHAR* argv[])
{Test1();Test2();Test3();return 0;
}

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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

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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

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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

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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);

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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.\n");exit(1);}pCurrent->m_pNext = pNext;
}void PrintListNode(ListNode* pNode)
{ if(pNode == NULL){printf("The node is NULL\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 != NULL){printf("%d\t", pNode->m_nValue);pNode = pNode->m_pNext;}printf("\nPrintList ends.\n");
}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;}
}

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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.

转载于:https://www.cnblogs.com/klchang/p/7590302.html