从尾到头打印单向链表

1.需求及分析

输入一个链表的头结点，从尾到头反过来打印出每个节点的值。

方法：

1.把链表中链接节点的指针反转过来，改变链表的方向，然后从头到尾输出。（实际上修改了链表的结构下下策）；

2.典型的先进后出，可以用“栈”处理；

3.典型的先进后出，由于递归和栈的处理方式接近也可以用递归处理。

2.使用栈处理

void PrintListReversingly_Iter(ListNode* pHead)
{
	std::stack<ListNode*> nodes; //定义链表指针栈区

	ListNode* pNode = pHead;     // 链表首地址指针
	while (pNode != NULL) //终止条件：链表地址指针为空
	{
		nodes.push(pNode);       //链表首地址指针压入栈区
		pNode = pNode->next;     //取下一个指针
	}

	while (!nodes.empty()) //终止条件：栈区为空
	{
		pNode = nodes.top();             //弹出链表指针
		cout << pNode->value<<"       "; //取出索引值
		nodes.pop();
	}
}

3.等效递归处理

void PrintListReversingly_Recur(ListNode* pHead)
{
	if (pHead != NULL)
	{
		if (pHead->next != NULL)
		{
			PrintListReversingly_Recur(pHead->next);
		}
		cout << pHead->value << "       "; 
	}
}

4.测试代码

/* list.h */
#include <stdio.h>  
#include <stdlib.h>  

struct ListNode{
	int value;
	ListNode* next;
};


ListNode* CreateListNode(int value){
	ListNode* pNode = new ListNode();
	pNode->value = value;
	pNode->next = NULL;
	return pNode;
}

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

	pCurrent->next = pNext;
}

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

void PrintList(ListNode* pHead){
	ListNode* pNode = pHead;
	while (pNode){
		printf("%d\t", pNode->value);
		pNode = pNode->next;
	}

	printf("\n");
}

void DestroyList(ListNode* pHead){
	ListNode* pNode = pHead;
	while (pNode){
		ListNode* pNext = pNode->next;
		delete pNode;
		pNode = pNext;
	}
}

void AddToTail(ListNode** pHead, int value){
	ListNode* pNode = new ListNode();
	pNode->value = value;
	pNode->next = NULL;

	if (*pHead == NULL)
		*pHead = pNode;
	else{
		ListNode* pCurrent = *pHead;
		while (pCurrent->next)
			pCurrent = pCurrent->next;

		pCurrent->next = pNode;
	}
}

void RemoveHead(ListNode** pHead, int value){
	if (pHead == NULL || *pHead == NULL)
		return;

	ListNode* pToBeDeleted = NULL;
	if ((*pHead)->value == value){
		pToBeDeleted = *pHead;
		*pHead = (*pHead)->next;
	}
	else{
		ListNode* pNode = *pHead;
		while (pNode->next != NULL && pNode->next->value != value)
			pNode = pNode->next;

		if (pNode->next != NULL && pNode->next->value == value){
			pToBeDeleted = pNode->next;
			pNode->next = pNode->next->next;
		}
	}

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

/* PrintReversingly */
#include <iostream>
#include "list.h"
#include <stack>
using namespace std;


void PrintListReversingly_Iter(ListNode* pHead)
{
	std::stack<ListNode*> nodes; //定义链表指针栈区

	ListNode* pNode = pHead;     // 链表首地址指针
	while (pNode != NULL) //终止条件：链表地址指针为空
	{
		nodes.push(pNode);       //链表首地址指针压入栈区
		pNode = pNode->next;     //取下一个指针
	}

	while (!nodes.empty()) //终止条件：栈区为空
	{
		pNode = nodes.top();             //弹出链表指针
		cout << pNode->value<<"       "; //取出索引值
		nodes.pop();
	}
}

void PrintListReversingly_Recur(ListNode* pHead)
{
	if (pHead != NULL)
	{
		if (pHead->next != NULL)
		{
			PrintListReversingly_Recur(pHead->next);
		}
		cout << pHead->value << "       "; 
	}
}
void Results(ListNode* pHead)
{
	PrintList(pHead);
	cout << endl;
	PrintListReversingly_Iter(pHead);
	cout << endl;
	PrintListReversingly_Recur(pHead);
}

void Test1()
{
	cout << endl;
	cout << "Test1 begins:" << endl;
	ListNode* pNode1 = CreateListNode(1);
	ListNode* pNode2 = CreateListNode(2);
	ListNode* pNode3 = CreateListNode(3);
	ListNode* pNode4 = CreateListNode(4);
	ListNode* pNode5 = CreateListNode(5);

	ConnectListNode(pNode1, pNode2);
	ConnectListNode(pNode2, pNode3);
	ConnectListNode(pNode3, pNode4);
	ConnectListNode(pNode4, pNode5);
	
	Results(pNode1);
	DestroyList(pNode1);
}

int main()
{
	Test1();
	return 0;
}