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Doubly Linked List (Data Structure) In C++
C++
C++ Language
Linked-list
Doubly-linked-list
Data Structures
Data Structures and Algorithms

A doubly-linked list is a linked data structure that consists of a set of sequentially linked records called nodes. Each node contains two fields, called links, that are references to the previous and to the next node in the sequence of nodes.

#include "stdio.h"
#include "conio.h"
#include "iostream.h"
using namespace std;
int insertdata(int x);
void display();
void deleteint(int x);
void reversel();
int searchint(int x);
int compare_fn(int a,int b)
{
    if(a>b)
        return 1;
    else if(b>a)
        return -1;
}
int compare_no=1;
struct node
{
int data;
node *prev;
node *next;
};
node *top = NULL;
int main()
{
    int ch,d,y;
    char ans='y';
    while(ans=='y')
    {
        cout<<"\n\t 1.Insert        2. Delete        3.Reverse      4.EXIT\nEnter Choice : ";
        cin>>ch;
        if(ch==1)
        {
            cout<<"Enter An Element To be inserted : ";
            cin>>d;
            d=insertdata(d);
            display();
        }
        else if(ch==2)
        {
            cout<<"Enter Element To Be Deleted : ";
            cin>>d;
            deleteint(d);
            display();
        }
        else if(ch==3)
            reversel();
        else
            return 0;
    }
    return 0;
}
int searchint(int x)
{
int count=0;
node *searchele=top;
while( searchele!=NULL)
{
    if(compare_fn(x,searchele->data)==compare_no)
    {
        searchele=searchele->next;
    count+=1;
    }
    else
        break;
}
return count;
}
int insertdata(int x)
{
    if(top==NULL)
    {
        top=new node;
        top->data=x;
        top->next=NULL;
        top->prev=NULL;
    }
    else if(compare_fn(top->data ,x)==compare_no)
    {
        node *n=new node;
        n->data=x;
        n->next=top;
        n->prev=NULL;
        top->prev=n;
        top=n;
    }
    else
    {
    int c=searchint(x);
    node *insertele=top;
    for(int i=0;i<c-1;i++)
        insertele=insertele->next;
    node *n=new node;
    n->data=x;
    node *b=insertele->next;
    node *N =insertele;
    n->prev=insertele;
    n->next=b;
    insertele->next=n;
    if(b!=NULL)
        b->prev=n;
    }
}
void display()
{
cout<<"Element In The Linked List Are : ";
node *disp=top;
while(disp!=NULL)
{
    cout<<" "<<disp->data;
    if(disp->next==NULL)
    {
        break;
    }
    disp=disp->next;
}
}
void deleteint(int x)
{
    node *del=top;
    if(del->data == x)
    {
        if(del->next==NULL && del->prev==NULL)
        {
            top=NULL;
            return;
        }
        del->next->prev=NULL;
        top=del->next;
    }
    else
    {
        node *delsuc=del->next;
        if(del==NULL)
        {
            cout<<"\nElement Not Found\n";
            return;
        }
            if(delsuc==NULL)
        {
            cout<<"\nElement Not Found\n";
            return;
        }
        while(delsuc->data != x)
        {
            del=del->next;
            delsuc=delsuc->next;
            if(del==NULL)
        {
            cout<<"\nElement Not Found\n";
            return;
        }
            if(delsuc==NULL)
        {
            cout<<"\nElement Not Found\n";
            return;
        }
        }
        del->next=delsuc->next;
        if(delsuc->next!=NULL)
        delsuc->next->prev=del;
    }
}
void reversel()
{
node *a=top;
node *b,*c,*d;
while(a!=NULL)
{
    d=a;
    c=a->next;
    b=a->prev;
    a->prev=a->next;
    a->next=b;
    a=c;
}
top=d;
cout<<"After Reversing the linked list";
display();
compare_no*=-1;
}

This is a doubly linked list program in C++. Each Node will have a reference pointer to its next as well as previous node.

It maintains an ascending order. So new elements are inserted in the right place.

Reversing A Linked List will reverse the list as well as the property Ascending becomes descending and vice-versa. So Order of various Process :

Insertion : O(n)

Deletion : O(n)

Reversal : O(n)

Search : O(n)

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