数据结构——线性表——链表反转

/**
*反转链表
**/ 

#include <cstdio>
#include <cstdlib> 
#include <iostream>

using namespace std;

typedef struct Node{
    int data;//数据域 
    struct Node* pNext;//指针域 
}NODE, *PNODE;//NODE等价于struct Node，PNODE等价于struct Node* 

//打印链表所有元素 
void print_list(PNODE pHead)
{
    pHead = pHead->pNext;
    while(pHead != NULL)
    {
        cout<<pHead->data<<" ";
        pHead = pHead->pNext;
    }
    cout<<endl;
    return;
}

//创建链表 
PNODE create_list()
{
    PNODE pHead = (PNODE)malloc(sizeof(NODE));
    PNODE pNow = pHead;
    
    for(int i=1; i<=5; i++)
    {
        PNODE pNew = (PNODE)malloc(sizeof(NODE));
        pNew->data = i;
        pNow->pNext = pNew;
        pNow = pNew;
    }
    pNow->pNext = NULL;
    return pHead;
}

//迭代反转链表 
void reverse_list(PNODE pHead)
{
    //首先定义三个变量
    PNODE pre = NULL;
    PNODE now = pHead->pNext;
    PNODE next = NULL;
    
    //反转 
    while(now != NULL)
    {
        next = now->pNext;//先保存下一个节点 
        now->pNext = pre;//当前节点的next指针指向前一个节点
        pre = now;//前一个节点赋值为当前节点 
        now = next;//当前节点赋值为下一个节点 
    }
    
    //最后把头结点指向新生成链表的头 
    pHead->pNext = pre;
    return; 
}

//递归反转链表 
PNODE reverse_list2(PNODE pHead)
{
    //一直递归直到找到尾节点 
    if(pHead == NULL || pHead->pNext == NULL)
        return pHead;
    
    PNODE pNew = reverse_list2(pHead->pNext);//返回的永远都是尾节点
    pHead->pNext->pNext = pHead;//让当前节点的下一个节点的指针指向当前节点 
    pHead->pNext = NULL;//让当前节点的下一个节点指向NULL 
    
    //返回的是原来链表的尾节点，也就是新链表的首节点 
    return pNew; 
}

int main() 
{
    PNODE pHead = NULL;
    pHead = create_list();
    print_list(pHead);
    
    cout<<"迭代反转链表之后"<<endl;
    reverse_list(pHead); 
    print_list(pHead);
    
    cout<<"递归反转链表之后"<<endl;
    pHead->pNext = reverse_list2(pHead->pNext);
    print_list(pHead);
    return 0;
}