Delete all occurrences of a given key in a linked list

Given a singly linked list, delete all occurrences of a given key in it. For example, consider the following list.

Input: 2 -> 2 -> 1 -> 8 -> 2 ->  3 ->  2 -> 7
       Key to delete = 2
Output:  1 -> 8 -> 3 -> 7 

This is mainly an extension of this post which deletes first occurrence of a given key.

We need to first check for all occurrences at head node and change the head node appropriately. Then we need to check for all occurrences inside a loop and delete them one by one. Following is the implementation for the same.

C

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// C Program to delete all occurrences of a given key in linked list
#include <stdio.h>
#include <stdlib.h>
  
// A linked list node
struct Node
{
    int data;
    struct Node *next;
};
  
/* Given a reference (pointer to pointer) to the head of a list
   and an int, inserts a new node on the front of the list. */
void push(struct Node** head_ref, int new_data)
{
    struct Node* new_node = (struct Node*) malloc(sizeof(struct Node));
    new_node->data  = new_data;
    new_node->next = (*head_ref);
    (*head_ref)    = new_node;
}
  
/* Given a reference (pointer to pointer) to the head of a list and
   a key, deletes all occurrence of the given key in linked list */
void deleteKey(struct Node **head_ref, int key)
{
    // Store head node
    struct Node* temp = *head_ref, *prev;
  
    // If head node itself holds the key or multiple occurrences of key
    while (temp != NULL && temp->data == key)
    {
        *head_ref = temp->next;   // Changed head
        free(temp);               // free old head
        temp = *head_ref;         // Change Temp
    }
  
    // Delete occurrences other than head
    while (temp != NULL)
    {
        // Search for the key to be deleted, keep track of the
        // previous node as we need to change 'prev->next'
        while (temp != NULL && temp->data != key)
        {
            prev = temp;
            temp = temp->next;
        }
  
        // If key was not present in linked list
        if (temp == NULL) return;
  
        // Unlink the node from linked list
        prev->next = temp->next;
  
        free(temp);  // Free memory
  
        //Update Temp for next iteration of outer loop
        temp = prev->next;
    }
}
  
// This function prints contents of linked list starting from
// the given node
void printList(struct Node *node)
{
    while (node != NULL)
    {
        printf(" %d ", node->data);
        node = node->next;
    }
}
  
/* Drier program to test above functions*/
int main()
{
    /* Start with the empty list */
    struct Node* head = NULL;
  
    push(&head, 7);
    push(&head, 2);
    push(&head, 3);
    push(&head, 2);
    push(&head, 8);
    push(&head, 1);
    push(&head, 2);
    push(&head, 2);
  
    int key = 2; // key to delete
  
    puts("Created Linked List: ");
    printList(head);
  
    deleteKey(&head, key);
    puts("\nLinked List after Deletion of 1: ");
  
    printList(head);
    return 0;
}

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Java

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// Java Program to delete all occurrences 
// of a given key in linked list
class LinkedList 
    static Node head; // head of list 
  
    /* Linked list Node*/
    class Node 
    
        int data; 
        Node next; 
        Node(int d) 
        
            data = d; 
            next = null
        
    
  
    /* Given a key, deletes all occurrence
    of the given key in linked list */
    void deleteKey(int key) 
    
        // Store head node 
        Node temp = head, prev = null
      
        // If head node itself holds the key 
        // or multiple occurrences of key 
        while (temp != null && temp.data == key) 
        
            head = temp.next; // Changed head 
            temp = head;         // Change Temp 
        
      
        // Delete occurrences other than head 
        while (temp != null
        
            // Search for the key to be deleted, 
            // keep track of the previous node 
            // as we need to change 'prev->next' 
            while (temp != null && temp.data != key) 
            
                prev = temp; 
                temp = temp.next; 
            
      
            // If key was not present in linked list 
            if (temp == null) return
      
            // Unlink the node from linked list 
            prev.next = temp.next; 
      
            //Update Temp for next iteration of outer loop 
            temp = prev.next; 
        
    
  
    /* Inserts a new Node at front of the list. */
    public void push(int new_data) 
    
        Node new_node = new Node(new_data); 
        new_node.next = head; 
        head = new_node; 
    
  
    /* This function prints contents of linked list 
    starting from the given node */
    public void printList() 
    
        Node tnode = head; 
        while (tnode != null
        
            System.out.print(tnode.data + " "); 
            tnode = tnode.next; 
        
    
  
    // Driver Code
    public static void main(String[] args) 
    
        LinkedList llist = new LinkedList(); 
  
        llist.push(7); 
        llist.push(2); 
        llist.push(3); 
        llist.push(2);
        llist.push(8); 
        llist.push(1); 
        llist.push(2); 
        llist.push(2);
  
        int key = 2; // key to delete 
  
        System.out.println("Created Linked list is:"); 
        llist.printList(); 
  
        llist.deleteKey(key);
  
        System.out.println("\nLinked List after Deletion is:"); 
        llist.printList(); 
    
  
// This code is contributed by Shubham

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Output:

Created Linked List:
 2  2  1  8  2  3  2  7
Linked List after Deletion of 1:
 1  8  3  7 

This article is contributed by Saransh. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.



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