链表交集、合并、排序

第四周

要求：

1、将两个有序的递增链表合并为一个递增的有序链表。要求结果链表仍使用原来两个链表的储存空间，不另外占用其他的储存空间。表中不允许有重复数据。

2、已知两个链表A和B分别表示两个集合，其元素递增排列。设计一个算法用于求出A与B的交集，并存放在A链表中。

思路：首先就是创建链表。一般有前插法和后插法；二要求递增的话可以用一个排序算法（简单看了一下冒泡排序）。三链表显示和销毁函数。

四重点就是合并和交集函数。注意就是对链表操作要释放多余的存储空间，比如：头结点，重复元素结点等

先定义结构

typedef struct LNode//定义结构
{
    int data;
    struct LNode *next;
}LNode, *Head;

一、创建链表(后插法)

Head Create(void)//创建链表
{
    LNode *head, *r, *p;
    head = new LNode;
    if (head == NULL)
        cout << "头结点创建失败!\n";
    p = head;
    int x, cycle = 1;
    while (cycle) {
        cout << "输入一个整数.\n";
        cin >> x;
        if (x != 0) {
            r = new LNode;
            r->data = x;
            p->next = r;
            p = r;
        }
        else {
            cycle = 0;
        }
    }
    p->next = NULL;
    cout << "链表创建成功！\n";
    return head;
}

二、排序（递增）

Head Order(Head head)//链表节点排序
{
    LNode *p = head->next, *q = head->next;
    if (!p)
        return head;
    int i = 0, temp = 0, flag = 1;
    while (q) {
        q = q->next;
        ++i;//数据节点个数i
    }
    while (flag && i >= 0) {//冒泡排序
        flag = 0;
        while (p->next != NULL) {
            if (p->data > p->next->data) {
                temp = p->data;
                p->data = p->next->data;
                p->next->data = temp;
                flag = 1;//标志置为1表示本轮有交换
            }
            p = p->next;
        }
        --i;
        p = head->next;//重新指向首元结点为下轮准备
    }
    return head;
}

三、链表显示

Status print(Head head)
{
    int i = 0;
    LNode *p = head;
    while (!p)
        return OK;
    while (p->next != NULL)
    {
        p = p->next;
        cout << p->data;
        cout << "   ";
        ++i;
    }
    cout << "   共有"<<i<<"个元素\n";
    return OK;
}

四、销毁链表

Status DestroyList(Head head)
{
    LNode *p;
    while (head->next != NULL)
    {
        p = head;
        head = head->next;
        delete p;
    }
    delete head;
    return OK;
}

五、链表交集

交集AB链表放入A链表中，释放B链表；head1为A链表，head2为B链表。

Head Intersection(Head head1, Head head2)//交集放入A链表
{
    LNode *head = NULL, *p1 = NULL, *p2 = NULL, *p = NULL;
    head = head1;
    //交集为空
    while (head1->next==NULL || head2->next==NULL) {
        while (head2->next != NULL)//A为空链表 直接删除B链表
        {
            p = head2;
            head2 = head2->next;
            delete p;
        }
            delete head2;
            return head1;
            break;
    }
    LNode *move = head, *temp = NULL;
    p1 = head1->next;
    p2 = head2->next;
    delete head2;
    //AB均不为空
    while (p1&&p2->next != NULL){
        if (p1->data < p2->data)
            p1 = p1->next;
        else if (p1->data > p2->data)
            p2 = p2->next;
        else if (p1->data == p2->data)
        {
            move->next = p1;
            move = p1;
            p1 = p1->next;
        }
    }
    if (p2->next == NULL) {//判断B链表最后一个结点
        if (p1->data == p2->data)
        {
            move->next = p1;
            move = p1;
            p1 = p1->next;
        }
    }
        move->next = NULL;//尾部指针为NULL
    return head;
}

六、链表合并

这里AB合并后放入B链表中。

Head Combine(Head head1, Head head2)//合并后放入B链表
{
    LNode *head=head2, *p1=NULL, *p2=NULL;
    if (head1->next==NULL) {//A为空链表或者AB都为空
        delete head1;
        return head2;
    }
    else if (head2->next == NULL) {//B为空链表
        head2->next = head1->next;//A链表赋给B链表
        delete head1;
        return head2;
    }
    p1 = head1->next;
    p2 = head2->next;
    delete head1;
    LNode *move = head, *temp = NULL;
    //按递增顺序依次链接
    while (p1&&p2) {
        if (p1->data < p2->data) {
            move->next = p1;
            move = p1;
            p1 = p1->next;
        }
        else if (p1->data > p2->data) {
            move->next = p2;
            move = p2;
            p2 = p2->next;
        }
        else if(p1->data == p2->data) {//相同数据只保存一个，p1p2向后移一位
            temp = p2;
            move->next = p1;
            move = p1;
            p1 = p1->next;
            p2 = p2->next;
            delete temp;//删除p2相同结点
        }

    }
    if (p1)//p2为NULL，直接连接p1后面的结点
        move->next = p1;
    if (p2)//p1为NULL，直接连接p2后面的结点
        move->next = p2;
    return head;
}

测试

int main()
{
    cout << "创建一个链表A. 输入0结束\n";
    Head head1 = Create();
    cout << "创建一个链表B. 输入0结束\n";
    Head head2 = Create();
    char ch;
    while (1) {
        cout << "---------------------------------------------------------------------------\n";
        cout << "+请选择要进行的操作:<a>显示A   <b>显示B   <c>交集AB   <d>合并AB   <x>退出+\n";
        cout << "---------------------------------------------------------------------------\n";
        ch = _getwch();
        if (ch == 'a') {
            cout << "A链表：";
            print(Order(head1));
        }
        else if (ch == 'b') {
            cout << "B链表：";
            print(Order(head2));
        }
        else if (ch == 'c') {
            cout << "AB交集为：";
            print(Order(Intersection(head1, head2)));
            cout << "输入任意字符结束\n";
            ch = _getwch();
            DestroyList(head1);
            break;
        }
        if (ch == 'd') {
            cout << "AB合并为：";
            print(Order(Combine(head1, head2)));
            cout << "输入任意字符结束\n";
            ch = _getwch();
            DestroyList(head2);
            break;
        }
        else if (ch == 'x') {
                break;
        }
    }

}

运行结果：

交集：

合并：

链表交集、合并、排序

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