Delete first occurrence of given Key from a Linked List
Last Updated :
15 May, 2023
Given a linked list and a key to be deleted. The task is to delete the first occurrence of the given key from the linked list.
Note: The list may have duplicates.
Examples:
Input: list = 1->2->3->5->2->10, key = 2
Output: 1->3->5->2->10
Explanation: There are two instances of 2. But as per the question we need to delete the first occurrence only.
Input: list = 3->3->3->3, key = 3
Output: 3->3->3
Approach:
The basic idea is to find the first occurrence of the key by traversing from the head and delete the node. The deletion of a node is explained in detail in Deletion in Linked List.
Follow the steps mentioned below to implement the idea:
- Start iterating from the given head of the linked list.
- If the data of the current node matches the given key, this is the first occurrence of the given key.
- So, delete this node and return the head of the modified linked list.
Below is the implementation of the above approach.
C
// A complete working C code to demonstrate
// deletion of given key in singly 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 a value, 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 the first occurrence
// of key in linked list
void deleteNode(struct Node** head_ref, int key)
{
// Store head node
struct Node *temp = *head_ref, *prev;
// If head node itself holds the key to be deleted
if (temp != NULL && temp->data == key) {
// Changed head
*head_ref = temp->next;
free(temp);
return;
}
// 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);
}
// 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;
}
}
// Driver code
int main()
{
// Start with the empty list
struct Node* head = NULL;
push(&head, 7);
push(&head, 1);
push(&head, 3);
push(&head, 2);
puts("Created Linked List: ");
printList(head);
deleteNode(&head, 1);
puts("\nLinked List after Deletion of 1: ");
printList(head);
return 0;
}
// A complete working C++ program to demonstrate
// deletion of given key in singly linked
#include <bits/stdc++.h>
using namespace std;
// A linked list node
class Node {
public:
int data;
Node* next;
};
// Given a reference (pointer to pointer) to the head
// of a list and a value, inserts a new node
// on the front of the list.
void push(Node** head_ref, int new_data)
{
Node* new_node = new 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
// the first occurrence of key in linked list
void deleteNode(Node** head_ref, int key)
{
// Store head node
Node* temp = *head_ref;
Node* prev = NULL;
// If head node itself holds
// the key to be deleted
if (temp != NULL && temp->data == key) {
// Changed head
*head_ref = temp->next;
// Free old head
delete temp;
return;
}
// Else Search for the key to be
// deleted, keep track of the
// previous node as we need to
// change 'prev->next'
else {
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 memory
delete temp;
}
}
// This function prints contents of
// linked list starting from the
// given node
void printList(Node* node)
{
while (node != NULL) {
cout << node->data << " ";
node = node->next;
}
}
// Driver code
int main()
{
// Start with the empty list
Node* head = NULL;
// Add elements in linked list
push(&head, 7);
push(&head, 1);
push(&head, 3);
push(&head, 2);
puts("Created Linked List: ");
printList(head);
deleteNode(&head, 1);
puts("\nLinked List after Deletion of 1: ");
printList(head);
return 0;
}
// A complete working Java program to demonstrate
// deletion of given key in singly linked list
import java.io.*;
public class LinkedList {
Node head;
// Linked list Node
class Node {
int data;
Node next;
Node(int d)
{
data = d;
next = null;
}
}
// Given a key, deletes the first
// occurrence of key in
// linked list
void deleteNode(int key)
{
// Store head node
Node temp = head, prev = null;
// If head node itself holds the key to be deleted
if (temp != null && temp.data == key) {
// Changed head
head = temp.next;
return;
}
// Search for the key to be deleted, keep track of
// the previous node as we need to change temp.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;
}
// 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 program to test above functions. Ideally this
// function should be in a separate user class. It is kept
// here to keep code compact
public static void main(String[] args)
{
LinkedList llist = new LinkedList();
llist.push(7);
llist.push(1);
llist.push(3);
llist.push(2);
System.out.println("Created Linked List:");
llist.printList();
// Delete node with data 1
llist.deleteNode(1);
System.out.println(
"\nLinked List after Deletion of 1:");
llist.printList();
}
}
# A complete working Python3 program to
# demonstrate deletion in singly
# linked list with class
# Node class
class Node:
# Constructor to initialize the node object
def __init__(self, data):
self.data = data
self.next = None
class LinkedList:
# Function to initialize head
def __init__(self):
self.head = None
# Function to insert a new node at the beginning
def push(self, new_data):
new_node = Node(new_data)
new_node.next = self.head
self.head = new_node
# Given a reference to the head of a list and a key,
# delete the first occurrence of key in linked list
def deleteNode(self, key):
# Store head node
temp = self.head
# If head node itself holds the key to be deleted
if (temp is not None):
if (temp.data == key):
self.head = temp.next
temp = None
return
# Search for the key to be deleted, keep track of the
# previous node as we need to change 'prev.next'
while(temp is not None):
if temp.data == key:
break
prev = temp
temp = temp.next
# If key was not present in linked list
if(temp == None):
return
# Unlink the node from linked list
prev.next = temp.next
temp = None
# Utility function to print the linked LinkedList
def printList(self):
temp = self.head
while(temp):
print(temp.data, end =" "),
temp = temp.next
# Driver code
if __name__ == '__main__':
llist = LinkedList()
llist.push(7)
llist.push(1)
llist.push(3)
llist.push(2)
print("Created Linked List:")
llist.printList()
llist.deleteNode(1)
print("\nLinked List after Deletion of 1:")
llist.printList()
// A complete working C# program
// to demonstrate deletion in
// singly linked list
using System;
class GFG {
// Head of list
Node head;
// Linked list Node
public class Node {
public int data;
public Node next;
public Node(int d)
{
data = d;
next = null;
}
}
// Given a key, deletes the first
// occurrence of key in linked list
void deleteNode(int key)
{
// Store head node
Node temp = head, prev = null;
// If head node itself holds
// the key to be deleted
if (temp != null && temp.data == key) {
// Changed head
head = temp.next;
return;
}
// Search for the key to be
// deleted, keep track of the
// previous node as we need
// to change temp.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;
}
// 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) {
Console.Write(tnode.data + " ");
tnode = tnode.next;
}
}
// Driver code
public static void Main(String[] args)
{
GFG llist = new GFG();
llist.Push(7);
llist.Push(1);
llist.Push(3);
llist.Push(2);
Console.WriteLine("Created Linked List:");
llist.printList();
// Delete node with data 1
llist.deleteNode(1);
Console.WriteLine(
"\nLinked List after Deletion of 1:");
llist.printList();
}
}
// A complete working javascript program
// to demonstrate deletion
// in singly linked list
// Head of list
var head;
// Linked list Node
class Node {
constructor(val) {
this.data = val;
this.next = null;
}
}
// Given a key, deletes the first occurrence
// of key in linked list
function deleteNode(key) {
// Store head node
var temp = head, prev = null;
// If head node itself holds the key to be deleted
if (temp != null && temp.data == key) {
// Changed head
head = temp.next;
return;
}
// Search for the key to be deleted, keep track of
// the previous node as we need to change temp.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;
}
// Inserts a new Node at front of the list.
function push(new_data) {
var 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
function printList() {
tnode = head;
while (tnode != null) {
console.log(tnode.data + " ");
tnode = tnode.next;
}
}
// Driver program to test above functions.
// Ideally this function should be in a
// separate user class. It is kept here to keep code compact
push(7);
push(1);
push(3);
push(2);
console.log("Created Linked List: ");
printList();
// Delete node with data 1
deleteNode(1);
console.log("Linked List after Deletion of 1:");
printList();
OutputCreated Linked List:
2 3 1 7
Linked List after Deletion of 1:
2 3 7
Time Complexity: O(N) where N is the length of the linked list
Auxiliary Space: O(1)
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