Data Structures - Circular Singly Linked List Other Related Topics
Data Structures - Circular Singly Linked List Other Related Topics

Circular Singly Linked List - Delete first node by key

In this method, first node in the circular singly linked list with specified key (value) is deleted. For example - if the given list is 10->20->30->10->20 and the first occurrence of 20 is deleted, the list becomes 10->30->10->20.

First, the head of the linked list is checked for null value. If the head is not null, the value stored in it is equal to the key, and head is the only element in the list then make the head as null. If the head is not null, the value stored in it is equal to the key, the list contains more than one element then make head next as head and update the link of last element of the list with the new head. Else, traverse to the node previous to the node with value equal to key, and adjust links.

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

void pop_first(int key) {
  
  //1. if head is not null, create two nodes- temp
  //   and nodeToDelete - to traverse and track 
  //   the node to delete  
  if(head != NULL) {
    Node* temp = head;
    Node* nodeToDelete = head;
    
    //2. if the value store at head is the key and head
    //   is the only element in the list, make it null
    if(temp->data == key) {
      if(temp->next == head) {
        head = NULL;
      } else {

        //3. if the value store at head is the key and list
        //   contains more than 1 elements, traverse to the
        //   last element of the list and link it to the new head
        while(temp->next != head) {
          temp = temp->next;
        }
        head = head->next;
        temp->next = head; 
        free(nodeToDelete); 
      }
    } else {
      
      //4. Else, traverse to the node previous to the 
      //   node with value equal to key, and adjust links 
      while(temp->next != head) {
        if(temp->next->data == key) {
          nodeToDelete = temp->next;
          temp->next = temp->next->next;
          free(nodeToDelete);
          break; 
        }
        temp = temp->next;
      }
    }
  }
}

void pop_first(struct Node** head_ref, int key) {
  
  //1. if head is not null, create two nodes- temp
  //   and nodeToDelete - to traverse and track 
  //   the node to delete  
  if(*head_ref != NULL) {
    struct Node* temp = *head_ref;
    struct Node* nodeToDelete = *head_ref;
    
    //2. if the value store at head is the key and head
    //   is the only element in the list, make it null
    if(temp->data == key) {
      if(temp->next == *head_ref) {
        *head_ref = NULL;
      } else {

        //3. if the value store at head is the key and list
        //   contains more than 1 elements, traverse to the
        //   last element of the list and link it to the new head
        while(temp->next != *head_ref) {
          temp = temp->next;
        }
        *head_ref = (*head_ref)->next;
        temp->next = *head_ref; 
        free(nodeToDelete); 
      }
    } else {
      
      //4. Else, traverse to the node previous to the 
      //   node with value equal to key, and adjust links 
      while(temp->next != *head_ref) {
        if(temp->next->data == key) {
          nodeToDelete = temp->next;
          temp->next = temp->next->next;
          free(nodeToDelete);
          break; 
        }
        temp = temp->next;
      }
    }
  }
}

def pop_first(self, key):
  
  #1. if head is not null, create two nodes- temp
  #   and nodeToDelete - to traverse and track 
  #   the node to delete  
  if(self.head != None):
    temp = self.head
    nodeToDelete = self.head
    
    #2. if the value store at head is the key and head
    #   is the only element in the list, make it null
    if(temp.data == key):
      if(temp.next == self.head):
        self.head = None
      else:

        #3. if the value store at head is the key and list
        #   contains more than 1 elements, traverse to the
        #   last element of the list and link it to the new head
        while(temp.next != self.head):
          temp = temp.next
        self.head = self.head.next
        temp.next = self.head
        nodeToDelete = None
    else:
      
      #4. Else, traverse to the node previous to the 
      #   node with value equal to key, and adjust links 
      while(temp.next != self.head):
        if(temp.next.data == key):
          nodeToDelete = temp.next
          temp.next = temp.next.next
          nodeToDelete = None
          break
        temp = temp.next

void pop_first(int key) {
  
  //1. if head is not null, create two nodes- temp
  //   and nodeToDelete - to traverse and track 
  //   the node to delete  
  if(this.head != null) {
    Node temp = this.head;
    Node nodeToDelete = this.head;
    
    //2. if the value store at head is the key and head
    //   is the only element in the list, make it null
    if(temp.data == key) {
      if(temp.next == this.head) {
        this.head = null;
      } else {

        //3. if the value store at head is the key and list
        //   contains more than 1 elements, traverse to the
        //   last element of the list and link it to the new head
        while(temp.next != this.head) {
          temp = temp.next;
        }
        this.head = this.head.next;
        temp.next = this.head; 
        nodeToDelete = null; 
      }
    } else {
      
      //4. Else, traverse to the node previous to the 
      //   node with value equal to key, and adjust links 
      while(temp.next != this.head) {
        if(temp.next.data == key) {
          nodeToDelete = temp.next;
          temp.next = temp.next.next;
          nodeToDelete = null;
          break; 
        }
        temp = temp.next;
      }
    }
  }
}

public void pop_first(int key) {
  
  //1. if head is not null, create two nodes- temp
  //   and nodeToDelete - to traverse and track 
  //   the node to delete  
  if(this.head != null) {
    Node temp = this.head;
    Node nodeToDelete = this.head;
    
    //2. if the value store at head is the key and head
    //   is the only element in the list, make it null
    if(temp.data == key) {
      if(temp.next == this.head) {
        this.head = null;
      } else {

        //3. if the value store at head is the key and list
        //   contains more than 1 elements, traverse to the
        //   last element of the list and link it to the new head
        while(temp.next != this.head) {
          temp = temp.next;
        }
        this.head = this.head.next;
        temp.next = this.head; 
        nodeToDelete = null; 
      }
    } else {
      
      //4. Else, traverse to the node previous to the 
      //   node with value equal to key, and adjust links 
      while(temp.next != this.head) {
        if(temp.next.data == key) {
          nodeToDelete = temp.next;
          temp.next = temp.next.next;
          nodeToDelete = null;
          break; 
        }
        temp = temp.next;
      }
    }
  }
}

public function pop_first($key) {
  
  //1. if head is not null, create two nodes- temp
  //   and nodeToDelete - to traverse and track 
  //   the node to delete  
  if($this->head != null) {
    $temp = $this->head;
    $nodeToDelete = $this->head;
    
    //2. if the value store at head is the key and head
    //   is the only element in the list, make it null
    if($temp->data == $key) {
      if($temp->next == $this->head) {
        $this->head = null;
      } else {

        //3. if the value store at head is the key and list
        //   contains more than 1 elements, traverse to the
        //   last element of the list and link it to the new head
        while($temp->next != $this->head) {
          $temp = $temp->next;
        }
        $this->head = $this->head->next;
        $temp->next = $this->head; 
        $nodeToDelete = null; 
      }
    } else {
      
      //4. Else, traverse to the node previous to the 
      //   node with value equal to key, and adjust links 
      while($temp->next != $this->head) {
        if($temp->next->data == $key) {
          $nodeToDelete = $temp->next;
          $temp->next = $temp->next->next;
          $nodeToDelete = null;
          break; 
        }
        $temp = $temp->next;
      }
    }
  }
}

The below is a complete program that uses above discussed concept to delete first occurrence of the specified key (if exists) 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 by key
    void pop_first(int key) {
      if(head != NULL) {
        Node* temp = head;
        Node* nodeToDelete = head;
	    
        if(temp->data == key) {
          if(temp->next == head) {
            head = NULL;
          } else {

            while(temp->next != head) {
              temp = temp->next;
            }
            head = head->next;
            temp->next = head; 
            free(nodeToDelete); 
          }
        } else {
          while(temp->next != head) {
            if(temp->next->data == key) {
              nodeToDelete = temp->next;
              temp->next = temp->next->next;
              free(nodeToDelete);
              break; 
            }
            temp = temp->next;
          }
        }
      }
    }

    //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 five elements in the list.
  MyList.push_back(10);
  MyList.push_back(20);
  MyList.push_back(30);
  MyList.push_back(10);
  MyList.push_back(20);
  MyList.PrintList();
  
  //Delete first occurrence of 20
  MyList.pop_first(20);
  MyList.PrintList();  
  
  return 0; 
}

The above code will give the following output: 

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

#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 by key
void pop_first(struct Node** head_ref, int key) {
  if(*head_ref != NULL) {
    struct Node* temp = *head_ref;
    struct Node* nodeToDelete = *head_ref;

    if(temp->data == key) {
      if(temp->next == *head_ref) {
        *head_ref = NULL;
      } else {

        while(temp->next != *head_ref) {
          temp = temp->next;
        }
        *head_ref = (*head_ref)->next;
        temp->next = *head_ref; 
        free(nodeToDelete); 
      }
    } else {
      
      while(temp->next != *head_ref) {
        if(temp->next->data == key) {
          nodeToDelete = temp->next;
          temp->next = temp->next->next;
          free(nodeToDelete);
          break; 
        }
        temp = temp->next;
      }
    }
  }
}

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

  //Delete first occurrence of 20
  pop_first(&MyList, 20);
  PrintList(MyList);

  return 0; 
}

The above code will give the following output: 

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

# 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 by key
  def pop_first(self, key):
    if(self.head != None):
      temp = self.head
      nodeToDelete = self.head
      if(temp.data == key):
        if(temp.next == self.head):
          self.head = None
        else:
          while(temp.next != self.head):
            temp = temp.next
          self.head = self.head.next
          temp.next = self.head
          nodeToDelete = None
      else: 
        while(temp.next != self.head):
          if(temp.next.data == key):
            nodeToDelete = temp.next
            temp.next = temp.next.next
            nodeToDelete = None
            break
          temp = temp.next

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

#Delete first occurrence of 20
MyList.pop_first(20)
MyList.PrintList()

The above code will give the following output: 

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

//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 by key
  void pop_first(int key) {
    if(this.head != null) {
      Node temp = this.head;
      Node nodeToDelete = this.head;
      if(temp.data == key) {
        if(temp.next == this.head) {
          this.head = null;
        } else {
          while(temp.next != this.head) {
            temp = temp.next;
          }
	      this.head = this.head.next;
          temp.next = this.head; 
          nodeToDelete = null; 
        }
      } else {
        while(temp.next != this.head) {
          if(temp.next.data == key) {
            nodeToDelete = temp.next;
            temp.next = temp.next.next;
            nodeToDelete = null;
            break; 
          }
          temp = temp.next;
        }
      }
    }
  }

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

    //Delete first occurrence of 20
    MyList.pop_first(20);
    MyList.PrintList(); 
  }
}

The above code will give the following output: 

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

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 by key
  public void pop_first(int key) {
    if(this.head != null) {
      Node temp = this.head;
      Node nodeToDelete = this.head;
      if(temp.data == key) {
        if(temp.next == this.head) {
          this.head = null;
        } else {
          while(temp.next != this.head) {
            temp = temp.next;
          }
	      this.head = this.head.next;
          temp.next = this.head; 
          nodeToDelete = null; 
        }
      } else {
        while(temp.next != this.head) {
          if(temp.next.data == key) {
            nodeToDelete = temp.next;
            temp.next = temp.next.next;
            nodeToDelete = null;
            break; 
          }
          temp = temp.next;
        }
      }
    }
  }

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

    //Delete first occurrence of 20
    MyList.pop_first(20);
    MyList.PrintList();  
  }
}

The above code will give the following output: 

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

<?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 by key
  public function pop_first($key) { 
    if($this->head != null) {
      $temp = $this->head;
      $nodeToDelete = $this->head;
      if($temp->data == $key) {
        if($temp->next == $this->head) {
          $this->head = null;
        } else {
          while($temp->next != $this->head) {
            $temp = $temp->next;
          }
          $this->head = $this->head->next;
          $temp->next = $this->head; 
          $nodeToDelete = null; 
        }
      } else {
        while($temp->next != $this->head) {
          if($temp->next->data == $key) {
            $nodeToDelete = $temp->next;
            $temp->next = $temp->next->next;
            $nodeToDelete = null;
            break; 
          }
          $temp = $temp->next;
        }
      }
    }
  }

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

//Delete first occurrence of 20
$MyList->pop_first(20);
$MyList->PrintList(); 
?>

The above code will give the following output: 

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