Question

What is a linked list? In this Discussion area, we will discuss another way to implement the list abstract data type, the linked list, and we will explore aspects such as the definition of a linked list, how to implement them in C++, uses, and the STL list.

Answer 1

A linked list is a linear data structure, in which the elements are not stored at contiguous memory locations. The elements in a linked list are linked using pointers as shown in the below image:

Abstract Data type (ADT) is a type (or class) for objects whose behaviour is defined by a set of value and a set of operations.

The definition of ADT only mentions what operations are to be performed but not how these operations will be implemented. It does not specify how data will be organized in memory and what algorithms will be used for implementing the operations. It is called “abstract” because it gives an implementation-independent view. The process of providing only the essentials and hiding the details is known as abstraction

List ADT

• The data is generally stored in key sequence in a list which has a head structure consisting of count, pointers and address of compare function needed to compare the data in the list.

//List ADT Type Definitions typedef struct node { void *DataPtr; struct node *link; } Node; typedef struct { int count; Node *pos; Node *head; Node *rear; int (*compare) (void *argument1, void *argument2) } LIST;

• The data node contains the pointer to a data structure and a self-referential pointer which points to the next node in the list.

Lists are sequence containers that allow non-contiguous memory allocation. As compared to vector, list has slow traversal, but once a position has been found, insertion and deletion are quick. Normally, when we say a List, we talk about doubly linked list. For implementing a singly linked list, we use forward list.

Below is the program to show the working of some functions of List:

#include <iostream>
#include <list>
#include <iterator>
using namespace std;

//function for printing the elements in a list
void showlist(list <int> g)
{
   list <int> :: iterator it;
   for(it = g.begin(); it != g.end(); ++it)
       cout << '\t' << *it;
   cout << '\n';
}

int main()
{

   list <int> gqlist1, gqlist2;

   for (int i = 0; i < 10; ++i)
   {
       gqlist1.push_back(i * 2);
       gqlist2.push_front(i * 3);
   }
   cout << "\nList 1 (gqlist1) is : ";
   showlist(gqlist1);

   cout << "\nList 2 (gqlist2) is : ";
   showlist(gqlist2);

   cout << "\ngqlist1.front() : " << gqlist1.front();
   cout << "\ngqlist1.back() : " << gqlist1.back();

   cout << "\ngqlist1.pop_front() : ";
   gqlist1.pop_front();
   showlist(gqlist1);

   cout << "\ngqlist2.pop_back() : ";
   gqlist2.pop_back();
   showlist(gqlist2);

   cout << "\ngqlist1.reverse() : ";
   gqlist1.reverse();
   showlist(gqlist1);

   cout << "\ngqlist2.sort(): ";
   gqlist2.sort();
   showlist(gqlist2);

   return 0;

}
OUTPUT:-

List 1 (gqlist1) is :     0    2    4    6    
8    10    12    14    16    18

List 2 (gqlist2) is :     27    24    21    18    
15    12    9    6    3    0

gqlist1.front() : 0
gqlist1.back() : 18
gqlist1.pop_front() :     2    4    6    8    
10    12    14    16    18

gqlist2.pop_back() :     27    24    21    18    
15    12    9    6    3

gqlist1.reverse() :     18    16    14    12    
10    8    6    4    2

gqlist2.sort():     3    6    9    12    
15    18    21    24    27