C++笔试题之实现单链表两两反转（置换）

本文链接：https://blog.csdn.net/caoshangpa/article/details/80362804
两两反转单链表就是把每两个数反转一次。如：

A -> B -> C ->D -> E -> F两两反转后变为 B -> A -> D ->C -> F -> E。

#include <iostream>
using namespace std;

struct Node{
    int data;
    Node* next;
};

void Display(Node *head)// 打印链表
{
    if (head == NULL)
    {
        cout << "the list is empty" << endl;
        return;
    }
    else
    {
        Node *p = head;
        while (p)
        {
            cout << p->data << " ";
            p = p->next;
        }
    }
    cout << endl;
}

Node* ReverseList(Node* head)// 两两反转链表
{
    if (head == NULL)
          return NULL;
    Node* cur = head;
    //记录下下个结点，下次的置换在该结点和该结点的下一个结点间进行
    Node * nexnex = cur->next->next;
    //置换当前结点和下一个结点，例如，这一步后B指向A了，但是A依然指向B，目标是要A指向D。
    Node * swaphead = cur->next;
    swaphead->next = cur;
    //递归,返回D
    Node * swapnexnex = ReverseList(nexnex);
    //使A指向D
    cur->next = swapnexnex;
    //最后返回B
    return swaphead;
}

Node* Init(int num) // 创建链表
{
    if (num <= 0)
        return NULL;
    Node* cur = NULL;
    Node* head = NULL;
    Node* node = (Node*)malloc(sizeof(Node));
    node->data = 1;
    head = cur = node;
    for (int i = 1; i < num; i++)
    {
        Node* node = (Node*)malloc(sizeof(Node));
        node->data = i + 1;
        cur->next = node;
        cur = node;
    }
    cur->next = NULL;
    return head;
}

int main( )
{
    Node* list = NULL;
    list = Init(10);
    Display(list);
    Node* newlist = ReverseList(list);
    Display(newlist);

    system("pause");
    return 0;
}

整个两两反转过程如下所示：