Write a function to delete a Linked List

Difficulty Level : Basic
Last Updated : 29 Nov, 2019

Algorithm For C/C++: Iterate through the linked list and delete all the nodes one by one. Main point here is not to access next of the current pointer if current pointer is deleted.

In Java, automatic garbage collection happens, so deleting a linked list is easy. We just need to change head to null.

Implementation:

C++

// C++ program to delete a linked list  
#include <bits/stdc++.h> 
using namespace std; 
  
/* Link list node */
class Node  
{  
    public: 
    int data;  
    Node* next;  
};  
  
/* Function to delete the entire linked list */
void deleteList(Node** head_ref)  
{  
      
/* deref head_ref to get the real head */
Node* current = *head_ref;  
Node* next;  
  
while (current != NULL)  
{  
    next = current->next;  
    free(current);  
    current = next;  
}  
      
/* deref head_ref to affect the real head back  
    in the caller. */
*head_ref = NULL;  
}  
  
/* Given a reference (pointer to pointer) to the head  
of a list and an int, push a new node on the front  
of the list. */
void push(Node** head_ref, int new_data)  
{  
    /* allocate node */
    Node* new_node = new Node(); 
  
    /* put in the data */
    new_node->data = new_data;  
      
    /* link the old list off the new node */
    new_node->next = (*head_ref);  
      
    /* move the head to point to the new node */
    (*head_ref) = new_node;  
}  
  
/* Driver code*/
int main()  
{  
    /* Start with the empty list */
    Node* head = NULL;  
      
    /* Use push() to construct below list  
    1->12->1->4->1 */
    push(&head, 1);  
    push(&head, 4);  
    push(&head, 1);  
    push(&head, 12);  
    push(&head, 1);  
      
    cout << "Deleting linked list";  
    deleteList(&head);  
      
    cout << "\nLinked list deleted";  
}  
  
// This is code is contributed by rathbhupendra 

C

// C program to delete a linked list 
#include<stdio.h> 
#include<stdlib.h> 
#include<assert.h> 
  
/* Link list node */
struct Node 
{ 
    int data; 
    struct Node* next; 
}; 
  
/* Function to delete the entire linked list */
void deleteList(struct Node** head_ref) 
{ 
   /* deref head_ref to get the real head */
   struct Node* current = *head_ref; 
   struct Node* next; 
  
   while (current != NULL)  
   { 
       next = current->next; 
       free(current); 
       current = next; 
   } 
    
   /* deref head_ref to affect the real head back 
      in the caller. */
   *head_ref = NULL; 
} 
  
/* Given a reference (pointer to pointer) to the head 
  of a list and an int, push a new node on the front 
  of the list. */
void push(struct Node** head_ref, int new_data) 
{ 
    /* allocate node */
    struct Node* new_node = 
            (struct Node*) malloc(sizeof(struct Node)); 
  
    /* put in the data  */
    new_node->data  = new_data; 
     
    /* link the old list off the new node */
    new_node->next = (*head_ref); 
     
    /* move the head to point to the new node */
    (*head_ref)    = new_node; 
} 
  
/* Driver program to test count function*/
int main() 
{ 
    /* Start with the empty list */
    struct Node* head = NULL; 
     
    /* Use push() to construct below list 
     1->12->1->4->1  */
    push(&head, 1); 
    push(&head, 4); 
    push(&head, 1);  
    push(&head, 12); 
    push(&head, 1);    
     
    printf("\n Deleting linked list"); 
    deleteList(&head);   
     
    printf("\n Linked list deleted"); 
} 

Java

// Java program to delete a linked list 
class LinkedList 
{ 
    Node head; // head of the list 
  
    /* Linked List node */
    class Node 
    { 
        int data; 
        Node next; 
        Node(int d) { data = d; next = null; } 
    } 
  
    /* Function deletes the entire linked list */
    void deleteList() 
    { 
        head = null; 
    } 
  
    /* Inserts a new Node at front of the list. */
    public void push(int new_data) 
    { 
        /* 1 & 2: Allocate the Node & 
                  Put in the data*/
        Node new_node = new Node(new_data); 
  
        /* 3. Make next of new Node as head */
        new_node.next = head; 
  
        /* 4. Move the head to point to new Node */
        head = new_node; 
    } 
  
    public static void main(String [] args) 
    { 
        LinkedList llist = new LinkedList(); 
        /* Use push() to construct below list 
           1->12->1->4->1  */
  
        llist.push(1); 
        llist.push(4); 
        llist.push(1); 
        llist.push(12); 
        llist.push(1); 
  
        System.out.println("Deleting the list"); 
        llist.deleteList(); 
  
        System.out.println("Linked list deleted"); 
    } 
} 
// This code is contributed by Rajat Mishra 

Python3

# Python3 program to delete all  
# the nodes of singly linked list 
  
# Node class 
class Node: 
  
    # Function to initialise the node object 
    def __init__(self, data): 
        self.data = data # Assign data 
        self.next = None # Initialize next as null 
  
  
# Constructor to initialize the node object 
class LinkedList: 
  
    # Function to initialize head 
    def __init__(self): 
        self.head = None
  
    def deleteList(self): 
          
        # initialize the current node 
        current = self.head 
        while current: 
            prev = current.next # move next node 
              
            # delete the current node 
            del current.data 
              
            # set current equals prev node 
            current = prev  
  
    # push function to add node in front of llist 
    def push(self, new_data): 
  
        # Allocate the Node & 
        # Put in the data 
        new_node = Node(new_data) 
          
        # Make next of new Node as head 
        new_node.next = self.head 
          
        # Move the head to point to new Node 
        self.head = new_node 
  
# Use push() to construct below  
# list 1-> 12-> 1-> 4-> 1   
if __name__ == '__main__': 
  
    llist = LinkedList() 
    llist.push(1) 
    llist.push(4) 
    llist.push(1) 
    llist.push(12) 
    llist.push(1) 
  
  
    print("Deleting linked list") 
    llist.deleteList() 
      
    print("Linked list deleted") 
  
  
# This article is provided by Shrikant13 

C#

// C# program to delete a linked list 
using System; 
      
public class LinkedList 
{ 
    Node head; // head of the list 
  
    /* Linked List node */
    class Node 
    { 
        public int data; 
        public Node next; 
        public Node(int d)  
        {  
            data = d; next = null; 
        } 
    } 
  
    /* Function deletes the entire linked list */
    void deleteList() 
    { 
        head = null; 
    } 
  
    /* Inserts a new Node at front of the list. */
    public void push(int new_data) 
    { 
        /* 1 & 2: Allocate the Node & 
                Put in the data*/
        Node new_node = new Node(new_data); 
  
        /* 3. Make next of new Node as head */
        new_node.next = head; 
  
        /* 4. Move the head to point to new Node */
        head = new_node; 
    } 
  
    // Driver code 
    public static void Main(String [] args) 
    { 
        LinkedList llist = new LinkedList(); 
        /* Use push() to construct below list 
        1->12->1->4->1 */
  
        llist.push(1); 
        llist.push(4); 
        llist.push(1); 
        llist.push(12); 
        llist.push(1); 
  
        Console.WriteLine("Deleting the list"); 
        llist.deleteList(); 
  
        Console.WriteLine("Linked list deleted"); 
    } 
} 
  
// This code has been contributed by Rajput-Ji  

Output:

 Deleting linked list
 Linked list deleted

Time Complexity: O(n)
Auxiliary Space: O(1)

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