Question

In C++

Write the definition for following methods of List data structure.

5. pushFront – The function appends an element in the list at the front. The operation increases the number of elements in the list by one.

6. pushback - The function appends an element in the list at the end. The operation increases the number of elements in the list by one.

7.popFront - The function returns and then removes an element in the list from the front. The operation decreases the number of elements in the list by one.

8.popBack - - The function returns and then removes an element in the list from the end. The operation decreases the number of elements in the list by one.

Answer 1

#include<iostream>
#include<bits/stdc++.h>
using namespace std;

struct Node
 {
    int val;
    struct Node *next;
    Node(int data)
      {
         val=data;
         next=NULL;
      }
 };

void pushFront(Node *&head, int data)
  {
     if(head==NULL)
       {
        head=new Node(data);
        return ;
       }
     struct Node *temp;
     temp = new Node(data);
     temp->next = head;
     head = temp;
  }

void pushback(Node *&head, int data)
  {
     if(head==NULL)
      {
        head = new Node(data);
        return ;
      }
     struct Node *cur=head;
     while(cur->next!=NULL)
       {
         cur = cur->next;
       }
     cur->next = new Node(data);
  }

void popFront(struct Node *&head)
  {
     if(head==NULL)
        return ;
     head=head->next;

  }

void popBack(struct Node *&head)
  {
     if(head==NULL)
        return ;
     struct Node *cur=head,*pre=NULL;

     while(cur->next!=NULL)
      {
         pre=cur;
         cur=cur->next;
      }
      if(pre)
        pre->next=NULL;
      else
        head=NULL;
  }

void display(struct Node *head)
 {
     if(head==NULL)
     return ;
     while(head!=NULL)
      {
          cout<<head->val<<" ";
          head=head->next;
      }
      cout<<endl;
 }

int main()
 {
   struct Node *head=NULL;

   pushFront(head, 5); // here it append 5  at the beginning in list.
   display(head);      //  5 is printed

   pushback(head, 3); // here it append 3 at end of list
   display(head);     // 5 3 is printed

   popFront(head);   // it pop 5 from the list
   display(head);    // 3 is printed

   popBack(head);    // it pop the element from the end of list
   display(head);    // nothing is printed.
 }

// This code is executable if any problem you will face to understand the code you can comment.