Given a singly linked list, delete all occurrences of a given key in it. For example, consider the following list.
Input: 2 -> 2 -> 4 -> 3 -> 2
Key to delete = 2
Output: 4 -> 3
This is mainly an alternative of this post which deletes multiple occurrences of a given key using separate condition loops for head and remaining nodes. Here we use a double pointer approach to use a single loop irrespective of the position of the element (head, tail or between). The original method to delete a node from a linked list without an extra check for the head was explained by Linus Torvalds in his “25th Anniversary of Linux” TED talk.
This article uses that logic to delete multiple recurrences of the key without an extra check for the head. Explanation: 1. Store address of head in a double pointer till we find a non “key” node. This takes care of the 1st while loop to handle the special case of the head. 2. If a node is not “key” node then store the address of node->next in pp. 3. if we find a “key” node later on then change pp (ultimately node->next) to point to current node->next. Following is C++ implementation for the same.
Implementation:
// CPP program to delete multiple // occurrences of a key using single // loop. #include <iostream> using namespace std;
// A linked list node struct Node {
int data;
struct Node* next;
}; struct Node* head = NULL;
void printList( struct Node* node)
{ while (node != NULL) {
printf ( " %d " , node->data);
node = node->next;
}
} void push( int new_data)
{ struct Node* new_node = new Node;
new_node->data = new_data;
new_node->next = (head);
(head) = new_node;
} void deleteEntry( int key)
{ // Start from head
struct Node** pp = &head;
while (*pp) {
struct Node* entry = *pp;
// If key found, then put
// next at the address of pp
// delete entry.
if (entry->data == key) {
*pp = entry->next;
delete (entry);
}
// Else move to next
else
pp = &(entry->next);
}
} int main()
{ push(2);
push(2);
push(4);
push(3);
push(2);
int key = 2; // key to delete
puts ( "Created Linked List: " );
printList(head);
printf ( "\n" );
deleteEntry(key);
printf ( "\nLinked List after Deletion of 2: \n" );
printList(head);
return 0;
} |
class Node {
int data;
Node next;
Node( int data) {
this .data = data;
this .next = null ;
}
} public class DeleteMultipleOccurrences {
static Node head = null ;
static void printList(Node node) {
while (node != null ) {
System.out.print( " " + node.data + " " );
node = node.next;
}
}
static void push( int newData) {
Node newNode = new Node(newData);
newNode.next = head;
head = newNode;
}
static void deleteEntry( int key) {
Node pp = head;
Node prev = null ;
while (pp != null ) {
Node entry = pp;
// If key found, then adjust next pointers
// and continue
if (entry.data == key) {
if (prev != null ) {
prev.next = entry.next;
} else {
head = entry.next;
}
} else {
prev = entry;
}
// Move to the next node
pp = entry.next;
}
}
public static void main(String[] args) {
push( 2 );
push( 2 );
push( 4 );
push( 3 );
push( 2 );
int key = 2 ; // key to delete
System.out.println( "Created Linked List:" );
printList(head);
System.out.println( "\nLinked List after Deletion of 2:" );
deleteEntry(key);
printList(head);
}
} |
# Python3 program to delete multiple # occurrences of a key using single # loop. class Node:
def __init__( self , data):
self .data = data
self . next = None
# Function to print the linked list def printList(node):
while node:
print (node.data, end = " " )
node = node. next
print ()
# Function to insert a new node at the beginning def push(new_data):
new_node = Node(new_data)
new_node. next = head
globals ()[ 'head' ] = new_node
# Function to delete all occurrences of a key def delete_entry(key):
global head
# Start from head
entry = head
prev = None
# Traverse the linked list
while entry:
# If key found, update the next of the previous node
if entry.data = = key:
if prev:
prev. next = entry. next
else :
head = entry. next
# Delete the current entry
del entry
# Move to the next node
entry = prev. next if prev else head
else :
# Move to the next node
prev = entry
entry = entry. next
# Driver code if __name__ = = '__main__' :
head = None
push( 2 )
push( 2 )
push( 4 )
push( 3 )
push( 2 )
key = 2 # key to delete
print ( "Created Linked List:" )
printList(head)
print ( "\nLinked List after Deletion of 2:" )
delete_entry(key)
printList(head)
# This code is contributed by shivamgupta0987654321 |
// C# program to delete multiple // occurrences of a key using single // loop. using System;
// A linked list node public class Node
{ public int data;
public Node next;
} public class LinkedList
{ static Node head = null ;
static void PrintList(Node node)
{
while (node != null )
{
Console.Write( " " + node.data + " " );
node = node.next;
}
}
static void Push( int newData)
{
Node newNode = new Node();
newNode.data = newData;
newNode.next = head;
head = newNode;
}
static void DeleteEntry( int key)
{
// Start from head
Node pp = head;
Node prev = null ;
while (pp != null )
{
// If key found, then skip the node
if (pp.data == key)
{
if (prev != null )
{
prev.next = pp.next;
}
else
{
head = pp.next;
}
pp = pp.next;
}
// Else move to next
else
{
prev = pp;
pp = pp.next;
}
}
}
public static void Main( string [] args)
{
Push(2);
Push(2);
Push(4);
Push(3);
Push(2);
int key = 2; // key to delete
Console.WriteLine( "Created Linked List: " );
PrintList(head);
Console.WriteLine();
DeleteEntry(key);
Console.WriteLine( "Linked List after Deletion of 2: " );
PrintList(head);
}
} |
// A linked list node class Node { constructor(data) {
this .data = data;
this .next = null ;
}
} let head = null ;
// Function to print the linked list function printList(node) {
while (node !== null ) {
console.log(` ${node.data} `);
node = node.next;
}
} // Function to insert a new node at the beginning of the linked list function push(new_data) {
const new_node = new Node(new_data);
new_node.next = head;
head = new_node;
} // Function to delete all occurrences of a key in the linked list function deleteEntry(key) {
let current = head;
let prev = null ;
while (current !== null ) {
if (current.data === key) {
if (prev === null ) {
head = current.next;
} else {
prev.next = current.next;
}
current = current.next;
} else {
prev = current;
current = current.next;
}
}
} // Insert some values into the linked list push(2); push(2); push(4); push(3); push(2); // Print the original linked list console.log( "Created Linked List: " );
printList(head); console.log( "\n" );
// Delete all occurrences of key = 2 const keyToDelete = 2; deleteEntry(keyToDelete); // Print the linked list after deletion console.log(`Linked List after Deletion of ${keyToDelete}: `); printList(head); |
Created Linked List: 2 3 4 2 2 Linked List after Deletion of 2: 3 4
Complexity Analysis:
- Time Complexity: O(n)
- Auxiliary Space: O(1), as no extra space is required