Delete a given node in Linked List under given constraints

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 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 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 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. Following are the implementation.

C++

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// 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 the first node */
    cout<<"\nDeleting first node "
    deleteNode(head, head); 
  
    cout<<"\nModified Linked List: "
    printList(head); 
    return 0; 
  
// This code is contributed by rathbhupendra

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C

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#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 the first node */
    printf("\nDeleting first node ");
    deleteNode(head, head);
  
    printf("\nModified Linked List: ");
    printList(head);
  
    getchar();
    return 0;
}

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Python 3

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# Node class
class Node:
  
    def __init__(self, data):
        self.data = data
        self.next = None
  
# LinkedList class
class LinkedList:
  
    def __init__(self):
        self.head = None
  
    def deleteNode(self, data):
        temp = self.head
  
        # if the element to be deleted is at the top 
        if (temp.data == data):
  
            if temp.next is not None:
                temp.data = temp.next.data
                temp.next = temp.next.next
            else:
                print("\nThere is only one node. \
                         The list can't be made empty")
            return
  
        # if not at top then we will search it one by one.
        while (temp.next is not None and 
               temp.next.data != data):
            temp = temp.next
              
        # if the temp->next is null
        # then element is not present
        if temp.next is None:
            print('\n Given node is not present in Linked List')
              
        # else element is present and we delete it
        else:
            temp.next = temp.next.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 Code
llist = 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

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Java

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// 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("");
  
        // Lets 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

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C#

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// C# program to delete a given 
// node in linked list under 
// given constraints
using 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("");
  
        // Lets 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

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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.



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