线性表---链式存储（双向链表）

本代码与上一代码单链表的极其相似，只是在插入删除操作中有所修改

注意：NULL是不可以有next结点和prior结点的（包括空表的表头，所以初始化链表只需head=NULL;一条语句），否则会导致调试过程异常终止。

//链式存储---双向链表
#include <iostream>
using namespace std;
//定义线性表类
class List {
private:
    //定义双向链表存储结构
    typedef struct LNode {
        int data;
        LNode *next;
        LNode *prior;
    };
    struct LNode *head;
public:
    //构造函数（初始化）
    List() {
        head = NULL;
    }
    //析构函数
    ~List() {
        LNode *p;
        if (head == NULL) return;
        p = head;
        LNode *q;
        while (p != NULL) {
            p->prior = NULL;
            q = p->next;
            delete p;
            p = q;
        }
    }
    //插入
    void insertList(int a,int k);
    //删除
    void deleteList(int k);
    //查找    
    //按数字查找
    LNode *findList(int a) {
        LNode *p;
        p = head;
        while (p != NULL&&p->data!=a) {
            p = p->next;
        }
        if (p->data == a) return p;
        else return NULL;
    }
    //按序号查找
    LNode *FindList(int k) {
        //判断序号是否符合条件
        LNode *q;
        if (k<1 || k>getLength()) {
            cout << "查找元素位置不符合条件，查找失败" << endl;
            return NULL;
        }
        int i = 1;
        q = head;
        while (q != NULL && i < k) {
            q = q->next;
            i++;
        }
        if (i == k) return q;
        else {
            cout << "查找失败" << endl;
            return NULL;
        }
    }
    //求线性表长度
    int getLength();
    //判断表是否为空
    bool isEmpty();
    //清空线性表
    void clearList();
};
void List::insertList(int a,int k) {
    //插入位置是否符合条件
    int n = getLength();
    if (k<1 || k>(n+1)) {
        cout << "所输入的插入位置不满足条件，无法进行插入操作" << endl;
        return;
    }
    LNode *s, *p, *q;
    s = (LNode*)malloc(sizeof(LNode));
    if (k == 1) {
        s->data = a;
        s->next = head;
        if(n!=0) head->prior = s;
        head = s;
        return;
    }
    else if (k <= n) {
        k = k - 1;
        p = FindList(k);
        q = p->next;
        s->data = a;
        s->next = q;
        s->prior = p;
        p->next = s;
        q->prior = s;
        return;
    }
    else{//尾结点
        p = FindList(k-1);
        if (p == NULL) {
            cout << "插入失败" << endl;
            return;
        }
        s->data = a;
        s->next = NULL;
        s->prior = p;
        p->next = s;
        return;
    }
}
void List::deleteList(int k) {
    //判断k是否符合条件
    if (k<1 || k>getLength()) {
        cout << "所要删除结点位置不符合条件" << endl;
        return;
    }
    LNode *p;
    if (k == 1) {
        p = head;
        head = head->next;
        head->prior = NULL;
        free(p);
        return;
    }
    LNode *s, *q;
        p = FindList(k - 1);
        s = p->next;
        if (k < getLength()) {
            q = s->next;
            p->next = q;
            q->prior = p;
        }
        else p->next = NULL;
        free(s);
        return;
}
int List::getLength() {
    LNode *p;
    int i = 0;
    p = head;
    while (p != NULL) {
        p = p->next;
        i++;
    }
    return i;
}
bool List::isEmpty() {
    if (getLength() == 0) return true;
    else
        return false;
}
void List::clearList() {
    //注意要释放每一个节点
    LNode *p;
    while (head != NULL) {
        p = head;
        head = head->next;
        free(p);
    }
}

int main() {
    List listA, listB;
    int i;
    cout << "开始进行插入操作" << endl;
    for (i = 1; i <= 10; i++) {
        listA.insertList(2 * i, i);
    }
    cout << "链表A插入操作结束" << endl;
    for (i = 1; i <= 10; i++) {
        listB.insertList(2 * i + 1, i);
    }
    cout << "链表B插入操作结束" << endl;
    //依次输出两个线性表的元素
    cout << "线性表A的元素如下" << endl;
    for (i = 1; i <=listA.getLength(); i++) cout << listA.FindList(i)->data << "     ";
    cout << endl;
    cout << "线性表B的元素如下" << endl;
    for (i = 1; i <= listB.getLength(); i++) cout << listB.FindList(i)->data << "      ";
    cout << endl;
    cout << "请输入要链表A删除的元素位置序号：";
    int n;
    cin >> n;
    listA.deleteList(n);
    cout << "删除节点后链表A内的元素依次为" << endl;
    for (i = 1; i <= listA.getLength(); i++) cout << listA.FindList(i)->data << "      ";
    cout << endl;
    return 0;
}

调试结果如下：