Delete a given node in Linked List under given constraints - GeeksforGeeks

22 Feb, 2022
Given a Singly Linked List, write a function to delete a given node. Your function must follow following constraints: 1) It must accept a pointer to the start node as the first parameter and node to be deleted as the second parameter i.e., a pointer to head node is not global. 2) It should not return a pointer to the head node. 3) It should not accept pointer to pointer to the head node.You may assume that the Linked List never becomes empty.Let the function name be deleteNode(). In a straightforward implementation, the function needs to modify the head pointer when the node to be deleted is the first node. As discussed in previous post, when a function modifies the head pointer, the function must use one of the given approaches, we can’t use any of those approaches here. Solution We explicitly handle the case when the node to be deleted is the first node, we copy the data of the next node to head and delete the next node. The cases when a deleted node is not the head node can be handled normally by finding the previous node and changing next of the previous node. The following are the implementation.  
C++
C
Python 3
Java
C#
Javascript
// C++ program to delete a given node// in linked list under given constraints#include <bits/stdc++.h>using namespace std; /* structure of a linked list node */class Node{    public:    int data;    Node *next;}; void deleteNode(Node *head, Node *n){    // When node to be deleted is head node    if(head == n)    {        if(head->next == NULL)        {            cout << "There is only one node." <<                    " The list can't be made empty ";            return;        }         /* Copy the data of next node to head */        head->data = head->next->data;         // store address of next node        n = head->next;         // Remove the link of next node        head->next = head->next->next;         // free memory        free(n);         return;    }      // When not first node, follow    // the normal deletion process     // find the previous node    Node *prev = head;    while(prev->next != NULL && prev->next != n)        prev = prev->next;     // Check if node really exists in Linked List    if(prev->next == NULL)    {        cout << "\nGiven node is not present in Linked List";        return;    }     // Remove node from Linked List    prev->next = prev->next->next;     // Free memory    free(n);     return;} /* Utility function to insert a node at the beginning */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;} /* Utility function to print a linked list */void printList(Node *head){    while(head!=NULL)    {        cout<<head->data<<" ";        head=head->next;    }    cout<<endl;} /* Driver code */int main(){    Node *head = NULL;     /* Create following linked list    12->15->10->11->5->6->2->3 */    push(&head,3);    push(&head,2);    push(&head,6);    push(&head,5);    push(&head,11);    push(&head,10);    push(&head,15);    push(&head,12);     cout<<"Given Linked List: ";    printList(head);     /* Let us delete the node with value 10 */    cout<<"\nDeleting node "<< head->next->next->data<<" ";    deleteNode(head, head->next->next);     cout<<"\nModified Linked List: ";    printList(head);     /* Let us delete the first node */    cout<<"\nDeleting first node ";    deleteNode(head, head);     cout<<"\nModified Linked List: ";    printList(head);    return 0;} // This code is contributed by rathbhupendra
#include <stdio.h>#include <stdlib.h> /* structure of a linked list node */struct Node{    int data;    struct Node *next;}; void deleteNode(struct Node *head, struct Node *n){    // When node to be deleted is head node    if(head == n)    {        if(head->next == NULL)        {            printf("There is only one node. The list can't be made empty ");            return;        }         /* Copy the data of next node to head */        head->data = head->next->data;         // store address of next node        n = head->next;         // Remove the link of next node        head->next = head->next->next;         // free memory        free(n);         return;    }      // When not first node, follow the normal deletion process     // find the previous node    struct Node *prev = head;    while(prev->next != NULL && prev->next != n)        prev = prev->next;     // Check if node really exists in Linked List    if(prev->next == NULL)    {        printf("\n Given node is not present in Linked List");        return;    }     // Remove node from Linked List    prev->next = prev->next->next;     // Free memory    free(n);     return;} /* Utility function to insert a node at the beginning */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;} /* Utility function to print a linked list */void printList(struct Node *head){    while(head!=NULL)    {        printf("%d ",head->data);        head=head->next;    }    printf("\n");} /* Driver program to test above functions */int main(){    struct Node *head = NULL;     /* Create following linked list      12->15->10->11->5->6->2->3 */    push(&head,3);    push(&head,2);    push(&head,6);    push(&head,5);    push(&head,11);    push(&head,10);    push(&head,15);    push(&head,12);     printf("Given Linked List: ");    printList(head);     /* Let us delete the node with value 10 */    printf("\nDeleting node %d: ", head->next->next->data);    deleteNode(head, head->next->next);     printf("\nModified Linked List: ");    printList(head);     /* Let us delete the first node */    printf("\nDeleting first node ");    deleteNode(head, head);     printf("\nModified Linked List: ");    printList(head);     getchar();    return 0;}
# Node classclass Node:     def __init__(self, data):        self.data = data        self.next = None # LinkedList classclass LinkedList:     def __init__(self):        self.head = None     def deleteNode(self, data):        temp = self.head        prev = self.head        if temp.data == data:            if temp.next is None:                print("Can't delete the node as it has only one node")            else:                temp.data = temp.next.data                temp.next = temp.next.next            return        while temp.next is not None and temp.data != data:            prev = temp            temp = temp.next        if temp.next is None and temp.data !=data:            print("Can't delete the node as it doesn't exist")         # If node is last node of the linked list        elif temp.next is None and temp.data == data:            prev.next = None        else:            prev.next = temp.next                           # To push a new element in the Linked List        def push(self, new_data):        new_node = Node(new_data)        new_node.next = self.head        self.head = new_node     # To print all the elements of the Linked List    def PrintList(self):         temp = self.head        while(temp):            print(temp.data, end = " ")            temp = temp.next # Driver Codellist = LinkedList()llist.push(3)llist.push(2)llist.push(6)llist.push(5)llist.push(11)llist.push(10)llist.push(15)llist.push(12) print("Given Linked List: ", end = ' ')llist.PrintList()print("\n\nDeleting node 10:")llist.deleteNode(10)print("Modified Linked List: ", end = ' ')llist.PrintList()print("\n\nDeleting first node")llist.deleteNode(12)print("Modified Linked List: ", end = ' ')llist.PrintList() # This code is contributed by Akarsh Somani
// Java program to delete a given node// in linked list under given constraints class LinkedList {     static Node head;     static class Node {         int data;        Node next;         Node(int d) {            data = d;            next = null;        }    }     void deleteNode(Node node, Node n) {                 // When node to be deleted is head node        if (node == n) {            if (node.next == null) {                System.out.println("There is only one node. The list "                                 + "can't be made empty ");                return;            }             /* Copy the data of next node to head */            node.data = node.next.data;             // store address of next node            n = node.next;             // Remove the link of next node            node.next = node.next.next;             // free memory            System.gc();             return;        }         // When not first node, follow the normal deletion process        // find the previous node        Node prev = node;        while (prev.next != null && prev.next != n) {            prev = prev.next;        }         // Check if node really exists in Linked List        if (prev.next == null) {            System.out.println("Given node is not present in Linked List");            return;        }         // Remove node from Linked List        prev.next = prev.next.next;         // Free memory        System.gc();         return;    }     /* Utility function to print a linked list */    void printList(Node head) {        while (head != null) {            System.out.print(head.data + " ");            head = head.next;        }        System.out.println("");    }     public static void main(String[] args) {        LinkedList list = new LinkedList();        list.head = new Node(12);        list.head.next = new Node(15);        list.head.next.next = new Node(10);        list.head.next.next.next = new Node(11);        list.head.next.next.next.next = new Node(5);        list.head.next.next.next.next.next = new Node(6);        list.head.next.next.next.next.next.next = new Node(2);        list.head.next.next.next.next.next.next.next = new Node(3);         System.out.println("Given Linked List :");        list.printList(head);        System.out.println("");                 // Let us delete the node with value 10        System.out.println("Deleting node :" + head.next.next.data);        list.deleteNode(head, head.next.next);         System.out.println("Modified Linked list :");        list.printList(head);        System.out.println("");         // Let us delete the first node        System.out.println("Deleting first Node");        list.deleteNode(head, head);        System.out.println("Modified Linked List");        list.printList(head);     }} // this code has been contributed by Mayank Jaiswal
// C# program to delete a given// node in linked list under// given constraintsusing System; public class LinkedList{     Node head;     class Node    {         public int data;        public Node next;         public Node(int d)        {            data = d;            next = null;        }    }     void deleteNode(Node node, Node n)    {                 // When node to be deleted is head node        if (node == n)        {            if (node.next == null)            {                Console.WriteLine("There is only one node. The list "                                + "can't be made empty ");                return;            }             /* Copy the data of next node to head */            node.data = node.next.data;             // store address of next node            n = node.next;             // Remove the link of next node            node.next = node.next.next;             // free memory            GC.Collect();             return;        }         // When not first node, follow        // the normal deletion process        // find the previous node        Node prev = node;        while (prev.next != null && prev.next != n)        {            prev = prev.next;        }         // Check if node really exists in Linked List        if (prev.next == null)        {            Console.WriteLine("Given node is not" +                               "present in Linked List");            return;        }         // Remove node from Linked List        prev.next = prev.next.next;         // Free memory        GC.Collect();         return;    }     /* Utility function to print a linked list */    void printList(Node head)    {        while (head != null)        {            Console.Write(head.data + " ");            head = head.next;        }        Console.WriteLine("");    }     // Driver code    public static void Main(String[] args)    {        LinkedList list = new LinkedList();        list.head = new Node(12);        list.head.next = new Node(15);        list.head.next.next = new Node(10);        list.head.next.next.next = new Node(11);        list.head.next.next.next.next = new Node(5);        list.head.next.next.next.next.next = new Node(6);        list.head.next.next.next.next.next.next = new Node(2);        list.head.next.next.next.next.next.next.next = new Node(3);         Console.WriteLine("Given Linked List :");        list.printList(list.head);        Console.WriteLine("");                 // Let us delete the node with value 10        Console.WriteLine("Deleting node :" +                            list.head.next.next.data);        list.deleteNode(list.head, list.head.next.next);         Console.WriteLine("Modified Linked list :");        list.printList(list.head);        Console.WriteLine("");         // Let us delete the first node        Console.WriteLine("Deleting first Node");        list.deleteNode(list.head, list.head);        Console.WriteLine("Modified Linked List");        list.printList(list.head);    }} // This code is contributed by Rajput-Ji
<script>// javascript program to delete a given node// in linked list under given constraintsvar head;      class Node     {            constructor(val)            {                this.data = val;                this.next = null;            }        }     function deleteNode( node,  n)    {         // When node to be deleted is head node        if (node == n)        {            if (node.next == null)            {                document.write("There is only one node. The list " + "can't be made empty ");                return;            }             /* Copy the data of next node to head */            node.data = node.next.data;             // store address of next node            n = node.next;             // Remove the link of next node            node.next = node.next.next;             // free memory                      return;        }         // When not first node, follow the normal deletion process        // find the previous node         prev = node;        while (prev.next != null && prev.next != n)        {            prev = prev.next;        }         // Check if node really exists in Linked List        if (prev.next == null)        {            document.write("Given node is not present in Linked List");            return;        }         // Remove node from Linked List        prev.next = prev.next.next;        return;    }     /* Utility function to print a linked list */    function printList( head)    {        while (head != null)        {            document.write(head.data + " ");            head = head.next;        }        document.write("");    }             head = new Node(12);        head.next = new Node(15);        head.next.next = new Node(10);        head.next.next.next = new Node(11);        head.next.next.next.next = new Node(5);        head.next.next.next.next.next = new Node(6);        head.next.next.next.next.next.next = new Node(2);        head.next.next.next.next.next.next.next = new Node(3);         document.write("Given Linked List :");        printList(head);        document.write("");         // Let us delete the node with value 10        document.write("<br/>Deleting node :" + head.next.next.data);        deleteNode(head, head.next.next);         document.write("<br/>Modified Linked list :");        printList(head);        document.write("<br/>");         // Let us delete the first node        document.write("Deleting first Node<br/>");        deleteNode(head, head);        document.write("Modified Linked List");        printList(head);  // This code is contributed by todaysgaurav</script>
Output:  
Given Linked List: 12 15 10 11 5 6 2 3

Deleting node 10:
Modified Linked List: 12 15 11 5 6 2 3

Deleting first node
Modified Linked List: 15 11 5 6 2 3
Please write comments if you find the above codes/algorithms incorrect, or find other ways to solve the same problem. 
Rajput-Ji
rathbhupendra
shubham_singh
akarshsomani
Akanksha_Rai
srinivasdasu
todaysgaurav
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