双向链表排序 c++

#include 

using namespace std;
//节点类型的定义
class Node
{
public:
    int data;
    Node *pre;
    Node *next;
    Node(int _data) : data(_data), pre(NULL), next(NULL)
    {
    }
};

void TwoWayBubble(Node *&L);
void CreateList(Node *&L, int n);
void Traverse(Node *L);

void TwoWayBubble(Node *&L)
{
    Node *head = L;    //头
    Node *tail = NULL; //尾
    Node *p = L->next;
    // Node *q;
    bool exchange = true; //是否交换,并且最后根据是否发生交换来判断循环是否结束

    while (exchange)
    {
        exchange = false;
        //大数沉底
        while (p->next != tail) //从左往右大数沉底
        {
            if (p->data > p->next->data)
            {
                exchange = true; //发生了交换
                swap(p->data, p->next->data);
            }

            p = p->next; //后移
        }

        //小数起泡
        while (p->pre != head) //从右往左小数冒泡
        {
            if (p->data < p->pre->data)
            {
                exchange = true; //发生了交换
                swap(p->data, p->pre->data);
            }

            p = p->pre; //前移
        }
    }
}

void CreateList(Node *&L, int n)
{
    Node *p = L; //p指向最后一个节点
    int a;
    for (int i = 0; i < n; i++)
    {
        cin >> a;
        Node *pNew = new Node(a); //分配一个新的节点空间;
        p->next = pNew;           //连接上上一个节点
        pNew->pre = p;            //新节点的前驱节点
        pNew->next = NULL;        //新节点的后继节点
        p = p->next;              //p更新
    }
}

void Traverse(Node *L)
{
    Node *p = L->next;
    while (p != NULL)
    {
        cout << p->data << " ";
        p = p->next;
    }
    cout << endl;
}

int main()
{
    int n; //数据元素个数

    //头结点的创建
    Node *L = new Node(-1); //分配一个节点的空间;
    //前驱后继均为空
    L->next = NULL;
    L->pre = NULL;

    cin >> n;

    CreateList(L, n); //链表的构建
    cout << "before sort: " << endl;
    Traverse(L);

    TwoWayBubble(L); //双向冒泡

    cout << "after sort: " << endl;
    Traverse(L); //遍历链表
    return 0;
}