Data Structures - Circular Singly Linked List Other Related Topics
Python Java C++ C C# PHP R SQL DS Algo InterviewQ

Circular Singly Linked List - Delete the first node



In this method, the first node of the circular singly linked list is deleted. For example - if the given list is 10->20->30->40 and the first node is deleted, the list becomes 20->30->40.

Deleting the first node of the circular singly linked list is very easy. If the list contains one node, delete the node. If the list contains more than one node, then create two nodes - temp and firstNode both pointing to the head. Using temp node, traverse to the last node of the list. Make next of head as the head node and next of last node as head. Finally, delete the first node.

Circular Singly Linked List - Delete First Node

The function pop_front is created for this purpose. It is a 4-step process.

void pop_front() {
  if(head != NULL) {
    
    //1. the list contains one node, delete
    //   make the head null
    if(head->next == head) {
      head = NULL;
    } else {
      
      //2. if the list contains more than one node,
      //   create two nodes - temp and firstNode, both
      //   pointing to head node
      Node* temp = head;
      Node* firstNode = head;
      
      //3. using temp node, traverse to the last node
      while(temp->next != head) {
        temp = temp->next;
      }
      
      //4. Make head as next of head,
      //   Make next of last node as head,
      //   delete the firstNode
      head = head->next;
      temp->next = head; 
      free(firstNode); 
    }
  }
}
void pop_front(struct Node** head_ref) {
  if(*head_ref != NULL) {
    
    //1. the list contains one node, delete
    //   make the head null
    if((*head_ref)->next == *head_ref) {
      *head_ref = NULL;
    } else {
      
      //2. if the list contains more than one node,
      //   create two nodes - temp and firstNode, both
      //   pointing to head node
      struct Node* temp = *head_ref;
      struct Node* firstNode = *head_ref;
      
      //3. using temp node, traverse to the last node
      while(temp->next != *head_ref) {
        temp = temp->next;
      }
      
      //4. Make head as next of head,
      //   Make next of last node as head,
      //   delete the firstNode
      *head_ref = (*head_ref)->next;
      temp->next = *head_ref; 
      free(firstNode); 
    } 
  }    
}
def pop_front(self):
  if(self.head != None):
    
    #1. the list contains one node, delete
    #   make the head null
    if(self.head.next == self.head):
      self.head = None
    else:
      
      #2. if the list contains more than one node,
      #   create two nodes - temp and firstNode, both
      #   pointing to head node
      temp = self.head
      firstNode = self.head

      #3. using temp node, traverse to the last node
      while(temp.next != self.head):
        temp = temp.next

      #4. Make head as next of head,
      #   Make next of last node as head,
      #   delete the firstNode
      self.head = self.head.next
      temp.next = self.head 
      firstNode = None 
void pop_front() {
  if(this.head != null) {
    
    //1. the list contains one node, delete
    //   make the head null
    if(this.head.next == this.head) {
      this.head = null;
    } else {
      
      //2. if the list contains more than one node,
      //   create two nodes - temp and firstNode, both
      //   pointing to head node
      Node temp = this.head;
      Node firstNode = this.head;
      
      //3. using temp node, traverse to the last node
      while(temp.next != this.head) {
        temp = temp.next;
      }
      
      //4. Make head as next of head,
      //   Make next of last node as head,
      //   delete the firstNode
      this.head = this.head.next;
      temp.next = this.head; 
      firstNode = null; 
    }
  }
}
public void pop_front() {
  if(this.head != null) {
    
    //1. the list contains one node, delete
    //   make the head null
    if(this.head.next == this.head) {
      this.head = null;
    } else {
      
      //2. if the list contains more than one node,
      //   create two nodes - temp and firstNode, both
      //   pointing to head node
      Node temp = this.head;
      Node firstNode = this.head;
      
      //3. using temp node, traverse to the last node
      while(temp.next != this.head) {
        temp = temp.next;
      }
      
      //4. Make head as next of head,
      //   Make next of last node as head,
      //   delete the firstNode
      this.head = this.head.next;
      temp.next = this.head; 
      firstNode = null; 
    }
  }
}
public function pop_front() {
  if($this->head != null) {
    
    //1. the list contains one node, delete
    //   make the head null
    if($this->head->next == $this->head) {
      $this->head = null;
    } else {
      
      //2. if the list contains more than one node,
      //   create two nodes - temp and firstNode, both
      //   pointing to head node
      $temp = $this->head;
      $firstNode = $this->head;
      
      //3. using temp node, traverse to the last node
      while($temp->next != $this->head) {
        $temp = $temp->next;
      }
      
      //4. Make head as next of head,
      //   Make next of last node as head,
      //   delete the firstNode
      $this->head = $this->head->next;
      $temp->next = $this->head; 
      $firstNode = null; 
    }
  }
}

The below is a complete program that uses above discussed concept of deleting the first node 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 end of the list
    void push_back(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;
      }    
    }

    //Delete first node of the list
    void pop_front() {
      if(head != NULL) {
        if(head->next == head) {
          head = NULL;
        } else {
          Node* temp = head;
          Node* firstNode = head;
          while(temp->next != head) {
            temp = temp->next;
          }
          head = head->next;
          temp->next = head; 
          free(firstNode); 
        }
      }
    }

    //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 four elements in the list.
  MyList.push_back(10);
  MyList.push_back(20);
  MyList.push_back(30);
  MyList.push_back(40);
  MyList.PrintList();
  
  //Delete the first node
  MyList.pop_front();
  MyList.PrintList();  
  
  return 0; 
}

The above code will give the following output:

The list contains: 10 20 30 40
The list contains: 20 30 40  
#include <stdio.h>
#include <stdlib.h>

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

//Add new element at the end of the list
void push_back(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;
  }
}

//Delete first node of the list
void pop_front(struct Node** head_ref) {
  if(*head_ref != NULL) {
    if((*head_ref)->next == *head_ref) {
      *head_ref = NULL;
    } else {
      struct Node* temp = *head_ref;
      struct Node* firstNode = *head_ref;
      while(temp->next != *head_ref) {
        temp = temp->next;
      }
      *head_ref = (*head_ref)->next;
      temp->next = *head_ref; 
      free(firstNode); 
    } 
  }    
}

//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 four elements in the list.
  push_back(&MyList, 10);
  push_back(&MyList, 20);
  push_back(&MyList, 30);
  push_back(&MyList, 40);
  PrintList(MyList);

  //Delete the first node
  pop_front(&MyList);
  PrintList(MyList);

  return 0; 
}

The above code will give the following output:

The list contains: 10 20 30 40
The list contains: 20 30 40  
# 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 end of the list
  def push_back(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

  #Delete first node of the list
  def pop_front(self):
    if(self.head != None):
      if(self.head.next == self.head):
        self.head = None
      else:
        temp = self.head
        firstNode = self.head
        while(temp.next != self.head):
          temp = temp.next
        self.head = self.head.next
        temp.next = self.head 
        firstNode = None 

  #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 four elements in the list.
MyList.push_back(10)
MyList.push_back(20)
MyList.push_back(30)
MyList.push_back(40)
MyList.PrintList()

#Delete the first node
MyList.pop_front()
MyList.PrintList()  

The above code will give the following output:

The list contains: 10 20 30 40
The list contains: 20 30 40  
//node structure
class Node {
    int data;
    Node next;
};

class LinkedList {
  Node head;

  LinkedList(){
    head = null;
  }

  //Add new element at the end of the list
  void push_back(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;
    }    
  }

  //Delete first node of the list
  void pop_front() {
    if(this.head != null) {
      if(this.head.next == this.head) {
        this.head = null;
      } else {
        Node temp = this.head;
        Node firstNode = this.head;
        while(temp.next != this.head) {
          temp = temp.next;
        }
        this.head = this.head.next;
        temp.next = this.head; 
        firstNode = null; 
      }
    }
  }

  //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 four elements in the list.
    MyList.push_back(10);
    MyList.push_back(20);
    MyList.push_back(30);
    MyList.push_back(40);
    MyList.PrintList(); 

    //Delete the first node
    MyList.pop_front();
    MyList.PrintList(); 
  }
}

The above code will give the following output:

The list contains: 10 20 30 40
The list contains: 20 30 40  
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 end of the list
  public void push_back(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;
    }    
  }

  //Delete first node of the list
  public void pop_front() {
    if(this.head != null) {
      if(this.head.next == this.head) {
        this.head = null;
      } else {
        Node temp = this.head;
        Node firstNode = this.head;
        while(temp.next != this.head) {
          temp = temp.next;
        }
        this.head = this.head.next;
        temp.next = this.head; 
        firstNode = null; 
      }
    }
  }

  //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 four elements in the list.
    MyList.push_back(10);
    MyList.push_back(20);
    MyList.push_back(30);
    MyList.push_back(40);
    MyList.PrintList();   

    //Delete the first node
    MyList.pop_front();
    MyList.PrintList();  
  }
}

The above code will give the following output:

The list contains: 10 20 30 40
The list contains: 20 30 40  
<?php
//node structure
class Node {
  public $data;
  public $next;
}

class LinkedList {
  public $head;

  public function __construct(){
    $this->head = null;
  }
  
  //Add new element at the end of the list
  public function push_back($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;
    }    
  }

  //Delete first node of the list
  public function pop_front() {
    if($this->head != null) {
      if($this->head->next == $this->head) {
        $this->head = null;
      } else {
        $temp = $this->head;
        $firstNode = $this->head;
        while($temp->next != $this->head) {
          $temp = $temp->next;
        }
        $this->head = $this->head->next;
        $temp->next = $this->head; 
        $firstNode = null; 
      }
    }
  }

  //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 four elements in the list.
$MyList->push_back(10);
$MyList->push_back(20);
$MyList->push_back(30);
$MyList->push_back(40);
$MyList->PrintList();

//Delete the first node
$MyList->pop_front();
$MyList->PrintList(); 
?>

The above code will give the following output:

The list contains: 10 20 30 40
The list contains: 20 30 40  

5