Data Structures - Circular Singly Linked List Other Related Topics
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Circular Singly Linked List - Insert a new node at the start



In this method, a new node is inserted at the start of the circular singly linked list. For example - if the given List is 10->20->30 and a new element 100 is added at the start, the List becomes 100->10->20->30.

Inserting a new node at the start of the circular singly linked list is very easy. First, a new node with given element is created. It is then added at the start of the list by linking the head node and last node to the new node.

Circular Singly Linked List - Add Node At Start

The function push_front is created for this purpose. It is a 6-step process.

void push_front(int newElement) {
  
  //1. allocate node
  Node* newNode = new Node();
  
  //2. assign data element
  newNode->data = newElement;
  
  //3. assign null to the next of new node
  newNode->next = NULL; 
  
  //4. Check the list is empty or not,
  //   if empty make the new node as head 
  if(head == NULL) {
    head = newNode;
    newNode->next = head;
  } else {
    
    //5. Else, traverse to the last node
    Node* temp = head;
    while(temp->next != head)
      temp = temp->next;
    
    //6. Adjust the links
    temp->next = newNode;
    newNode->next = head;
    head = newNode;
  }    
}
void push_front(struct Node** head_ref, int newElement) {  
  
  //1. allocate node
  struct Node *newNode, *temp;
  newNode = (struct Node*)malloc(sizeof(struct Node)); 
  
  //2. assign data element
  newNode->data = newElement;  
  
  //3. assign null to the next of new node
  newNode->next = NULL;
  
  //4. Check the list is empty or not,
  //   if empty make the new node as head 
  if(*head_ref == NULL) {
    *head_ref = newNode;
    newNode->next = *head_ref;
  } else {
    
    //5. Else, traverse to the last node
    temp = *head_ref;
    while(temp->next != *head_ref) {
      temp = temp->next;
    }    
    
    //6. Adjust the links
    temp->next = newNode;
    newNode->next = *head_ref;
    *head_ref = newNode;
  }
}
def push_front(self, newElement):
  
  #1 & 2 & 3. allocate node, assign data element
  #          assign null to the next of new node
  newNode = Node(newElement)
  
  #4. Check the list is empty or not,
  #   if empty make the new node as head 
  if(self.head == None):
    self.head = newNode
    newNode.next = self.head
    return
  else:
    
    #5. Else, traverse to the last node
    temp = self.head
    while(temp.next != self.head):
      temp = temp.next
    
    #6. Adjust the links  
    temp.next = newNode
    newNode.next = self.head
    self.head = newNode
void push_front(int newElement) {
  
  //1. allocate node
  Node newNode = new Node();
  
  //2. assign data element
  newNode.data = newElement;
  
  //3. assign null to the next of new node
  newNode.next = null; 
  
  //4. Check the list is empty or not,
  //   if empty make the new node as head 
  if(head == null) {
    head = newNode;
    newNode.next = head;
  } else {
    
    //5. Else, traverse to the last node
    Node temp = new Node();
    temp = head;
    while(temp.next != head)
      temp = temp.next;
    
    //6. Adjust the links
    temp.next = newNode;
    newNode.next = head;
    head = newNode;
  }    
}
public void push_front(int newElement) {
  
  //1. allocate node
  Node newNode = new Node();
  
  //2. assign data element
  newNode.data = newElement;
  
  //3. assign null to the next of new node
  newNode.next = null; 
  
  //4. Check the list is empty or not,
  //   if empty make the new node as head
  if(head == null) {
    head = newNode;
    newNode.next = head;
  } else {
    
    //5. Else, traverse to the last node
    Node temp = new Node();
    temp = head;
    while(temp.next != head)
      temp = temp.next;
    
    //6. Adjust the links
    temp.next = newNode;
    newNode.next = head;
    head = newNode;
  }    
}
public function push_front($newElement) {
  
  //1. allocate node
  $newNode = new Node();
  
  //2. assign data element
  $newNode->data = $newElement;
  
  //3. assign null to the next of new node
  $newNode->next = null; 
  
  //4. Check the list is empty or not,
  //   if empty make the new node as head 
  if($this->head == null) {
    $this->head = $newNode;
    $newNode->next = $this->head;
  } else {
    
    //5. Else, traverse to the last node
    $temp = new Node();
    $temp = $this->head;
    while($temp->next !== $this->head) {
      $temp = $temp->next;
    }
    
    //6. Adjust the links
    $temp->next = $newNode;
    $newNode->next = $this->head;
    $this->head = $newNode;
  }    
}

The below is a complete program that uses above discussed concept to insert new node at the start of the circular singly linked list.

#include <iostream>
using namespace std;

//node structure
struct Node {
    int data;
    Node* next;
};

class LinkedList {
  private:
    Node* head;
  public:
    LinkedList(){
      head = NULL;
    }
 
    //Add new element at the start of the list
    void push_front(int newElement) {
      Node* newNode = new Node();
      newNode->data = newElement;
      newNode->next = NULL; 
      if(head == NULL) {
        head = newNode;
        newNode->next = head;
      } else {
        Node* temp = head;
        while(temp->next != head)
          temp = temp->next;
        temp->next = newNode;
        newNode->next = head;
        head = newNode;
      }    
    }

    //display the content of the list
    void PrintList() {
      Node* temp = head;
      if(temp != NULL) {
        cout<<"The list contains: ";
        while(true) {
          cout<<temp->data<<" ";
          temp = temp->next;
          if(temp == head) 
            break;
        }
        cout<<endl;
      } else {
        cout<<"The list is empty.\n";
      }
    }     
};

// test the code 
int main() {
  LinkedList MyList;

  //Add three elements at the start of the list.
  MyList.push_front(10);
  MyList.push_front(20);
  MyList.push_front(30);
  MyList.PrintList();
  
  return 0; 
}

The above code will give the following output:

The list contains: 30 20 10 
#include <stdio.h>
#include <stdlib.h>

//node structure
struct Node {
  int data;
  struct Node* next;
};

//Add new element at the start of the list
void push_front(struct Node** head_ref, int newElement) {  
  struct Node *newNode, *temp;
  newNode = (struct Node*)malloc(sizeof(struct Node)); 
  newNode->data = newElement;  
  newNode->next = NULL;
  if(*head_ref == NULL) {
    *head_ref = newNode;
    newNode->next = *head_ref;
  } else {
    temp = *head_ref;
    while(temp->next != *head_ref) {
      temp = temp->next;
    }    
    temp->next = newNode;
    newNode->next = *head_ref;
    *head_ref = newNode;
  }
}

//display the content of the list
void PrintList(struct Node* head_ref) {
  struct Node* temp = head_ref;
  if(head_ref != NULL) {
    printf("The list contains: ");
    while (1) {
      printf("%i ",temp->data);
      temp = temp->next;
      if(temp == head_ref)
        break;    
    }
    printf("\n");
  } else {
    printf("The list is empty.\n");
  }   
}

// test the code 
int main() {
  struct Node* MyList = NULL;

  //Add three elements at the start of the list.
  push_front(&MyList, 10);
  push_front(&MyList, 20);
  push_front(&MyList, 30);
  PrintList(MyList);

  return 0; 
}

The above code will give the following output:

The list contains: 30 20 10 
# node structure
class Node:
  def __init__(self, data):
    self.data = data
    self.next = None

#class Linked List
class LinkedList:
  def __init__(self):
    self.head = None

  #Add new element at the start of the list
  def push_front(self, newElement):
    newNode = Node(newElement)
    if(self.head == None):
      self.head = newNode
      newNode.next = self.head
      return
    else:
      temp = self.head
      while(temp.next != self.head):
        temp = temp.next
      temp.next = newNode
      newNode.next = self.head
      self.head = newNode

  #display the content of the list
  def PrintList(self):
    temp = self.head
    if(temp != None):
      print("The list contains:", end=" ")
      while (True):
        print(temp.data, end=" ")
        temp = temp.next
        if(temp == self.head):
          break
      print()
    else:
      print("The list is empty.")

# test the code                  
MyList = LinkedList()

#Add three elements at the start of the list.
MyList.push_front(10)
MyList.push_front(20)
MyList.push_front(30)
MyList.PrintList()

The above code will give the following output:

The list contains: 30 20 10 
//node structure
class Node {
    int data;
    Node next;
};

class LinkedList {
  Node head;

  LinkedList(){
    head = null;
  }

  //Add new element at the start of the list
  void push_front(int newElement) {
    Node newNode = new Node();
    newNode.data = newElement;
    newNode.next = null; 
    if(head == null) {
      head = newNode;
      newNode.next = head;
    } else {
      Node temp = new Node();
      temp = head;
      while(temp.next != head)
        temp = temp.next;
      temp.next = newNode;
      newNode.next = head;
      head = newNode;
    }    
  }

  //display the content of the list
  void PrintList() {
    Node temp = new Node();
    temp = this.head;
    if(temp != null) {
      System.out.print("The list contains: ");
      while(true) {
        System.out.print(temp.data + " ");
        temp = temp.next;
        if(temp == this.head)
          break;
      }
      System.out.println();
    } else {
      System.out.println("The list is empty.");
    }
  }     
};

// test the code 
public class Implementation {
  public static void main(String[] args) {
    LinkedList MyList = new LinkedList();

    //Add three elements at the start of the list.
    MyList.push_front(10);
    MyList.push_front(20);
    MyList.push_front(30);
    MyList.PrintList(); 
  }
}

The above code will give the following output:

The list contains: 30 20 10 
using System;

//node structure
class Node {
  public int data;
  public Node next;
};

class LinkedList {
  Node head;

  public LinkedList(){
    head = null;
  }
  
  //Add new element at the start of the list
  public void push_front(int newElement) {
    Node newNode = new Node();
    newNode.data = newElement;
    newNode.next = null; 
    if(head == null) {
      head = newNode;
      newNode.next = head;
    } else {
      Node temp = new Node();
      temp = head;
      while(temp.next != head)
        temp = temp.next;
      temp.next = newNode;
      newNode.next = head;
      head = newNode;
    }    
  }

  //display the content of the list
  public void PrintList() {
    Node temp = new Node();
    temp = this.head;
    if(temp != null) {
      Console.Write("The list contains: ");
      while(true) {
        Console.Write(temp.data + " ");
        temp = temp.next;
        if(temp == this.head)
          break;        
      }
      Console.WriteLine();
    } else {
      Console.WriteLine("The list is empty.");
    }
  }      
};

// test the code
class Implementation {  
  static void Main(string[] args) {
    LinkedList MyList = new LinkedList();

    //Add three elements at the start of the list.
    MyList.push_front(10);
    MyList.push_front(20);
    MyList.push_front(30);
    MyList.PrintList();   
  }
}

The above code will give the following output:

The list contains: 30 20 10 
<?php
//node structure
class Node {
  public $data;
  public $next;
}

class LinkedList {
  public $head;

  public function __construct(){
    $this->head = null;
  }
  
  //Add new element at the start of the list
  public function push_front($newElement) {
    $newNode = new Node();
    $newNode->data = $newElement;
    $newNode->next = null; 
    if($this->head == null) {
      $this->head = $newNode;
      $newNode->next = $this->head;
    } else {
      $temp = new Node();
      $temp = $this->head;
      while($temp->next !== $this->head) {
        $temp = $temp->next;
      }
      $temp->next = $newNode;
      $newNode->next = $this->head;
      $this->head = $newNode;
    }    
  }

  //display the content of the list
  public function PrintList() {
    $temp = new Node();
    $temp = $this->head;
    if($temp != null) {
      echo "The list contains: ";
      while(true) {
        echo $temp->data." ";
        $temp = $temp->next;
        if($temp == $this->head)
          break;        
      }
      echo "\n";
    } else {
      echo "The list is empty.\n";
    }
  }    
};

// test the code  
$MyList = new LinkedList();

//Add three elements at the start of the list.
$MyList->push_front(10);
$MyList->push_front(20);
$MyList->push_front(30);
$MyList->PrintList();
?>

The above code will give the following output:

The list contains: 30 20 10 

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