数据结构一双链表

//双链表
#include<iostream>
using namespace std;
typedef struct DNode{
    int data;
    struct DNode *prev;
    struct DNode *next;
}DNode,*DLinkList;

//初始化链表
void InitDLinkList(DLinkList &D){
    D = new DNode;
    D->prev = nullptr;
    D->prev = nullptr;
}

//遍历链表
void Print_D(DLinkList &D){
    DLinkList p = D->next;
    if(D == NULL || D->next == NULL){
        cout<<"双链表为空"<<endl;
        return;
    }

    while(p != nullptr){
        cout<<p->data<<"  ";
        p = p->next;
    }
    cout<<endl;
}


//在D中第i个元素之前插入数据元素e
int Insert_D(DLinkList &D,int i,int e){
    DLinkList p = D;
    int j = 0;

    while(p != nullptr && j<i-1){
        p = p->next;//找到第i-1个元素
        j++;
    }

    if(p == nullptr || j>i-1){
        return -1;
    }

    DLinkList s = new DNode;
    s->data = e;

    //先更新新结点的前去和后继指针
    s->next = p->next;
    s->prev = p;

    //再更新原链表中相邻结点的前驱和后继指针
    if(p->next != nullptr){
        p->next->prev = s;
    }
    p->next = s;


    return 1;
}

int main() {
    DLinkList L;
    InitDLinkList(L);
    Insert_D(L, 1, 1);
    Insert_D(L, 2, 2);
    Insert_D(L, 3, 3);
    Insert_D(L, 4, 4);
    Insert_D(L, 5, 5);
    cout << "双链表: ";
    Print_D(L);

    Insert_D(L, 3, 10);  // 在第3个元素之前插入10
    cout << "插入10后的双链表: ";
    Print_D(L);

    return 0;
}