Delete last occurrence of an item from linked list

Loop through the whole list and use a double pointer to keep track of the node containing the address of last occurrence node.

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#include <stdio.h>
#include <stdlib.h>
  
// A linked list Node
struct Node {
    int data;
    struct Node* next;
};
  
// Function to delete the last occurrence
void deleteLast(struct Node** head, int x)
{
        struct Node** tmp1 = NULL;
        while(*head) {
                if((*head)->data == x) {
                        tmp1 = head;
                }
                head = &(*head)->next;
        }
        if(tmp1) {
                struct Node* tmp = *tmp1;
                *tmp1 = tmp->next;
                free(tmp);
        }
}
  
/* Utility function to create a new node with
given key */
struct Node* newNode(int x)
{
    struct Node* node = malloc(sizeof(struct Node*));
    node->data = x;
    node->next = NULL;
    return node;
}
  
// This function prints contents of linked list
// starting from the given Node
void display(struct Node* head)
{
    struct Node* temp = head;
    if (head == NULL) {
        printf("NULL\n");
        return;
    }
    while (temp != NULL) {
        printf("%d --> ", temp->data);
        temp = temp->next;
    }
    printf("NULL\n");
}
  
/* Drier program to test above functions*/
int main()
{
    struct Node* head = newNode(1);
    head->next = newNode(2);
    head->next->next = newNode(3);
    head->next->next->next = newNode(4);
    head->next->next->next->next = newNode(5);
    head->next->next->next->next->next = newNode(4);
    head->next->next->next->next->next->next = newNode(4);
    printf("Created Linked list: ");
    display(head);
    deleteLast(&head, 4);   // Pass the address of the head pointer
    printf("List after deletion of 4: ");
    display(head);
    return 0;
}

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Given a liked list and a key to be deleted. Delete last occurrence of key from linked. The list may have duplicates.

Examples:



Input:   1->2->3->5->2->10, key = 2
Output:  1->2->3->5->10

The idea is to traverse the linked list from beginning to end. While traversing, keep track of last occurrence key. After traversing the complete list, delete last occurrence by copying data of next node and deleting the next node.

C++

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// A C++ program to demonstrate deletion of last
// Node in singly linked list
#include <bits/stdc++.h>
  
// A linked list Node
struct Node {
    int key;
    struct Node* next;
};
  
void deleteLast(Node* head, int key)
{
    // Initialize previous of Node to be deleted
    Node* x = NULL;
  
    // Start from head and find the Node to be
    // deleted
    Node* temp = head;
    while (temp) {
        // If we found the key, update xv
        if (temp->key == key)
            x = temp;
  
        temp = temp->next;
    }
  
    // key occurs at-least once
    if (x != NULL) {
  
        // Copy key of next Node to x
        x->key = x->next->key;
  
        // Store and unlink next
        temp = x->next;
        x->next = x->next->next;
  
        // Free memory for next
        delete temp;
    }
}
  
/* Utility function to create a new node with
   given key */
Node* newNode(int key)
{
    Node* temp = new Node;
    temp->key = key;
    temp->next = NULL;
    return temp;
}
  
// This function prints contents of linked list
// starting from the given Node
void printList(struct Node* node)
{
    while (node != NULL) {
        printf(" %d ", node->key);
        node = node->next;
    }
}
  
/* Drier program to test above functions*/
int main()
{
    /* Start with the empty list */
    struct Node* head = newNode(1);
    head->next = newNode(2);
    head->next->next = newNode(3);
    head->next->next->next = newNode(5);
    head->next->next->next->next = newNode(2);
    head->next->next->next->next->next = newNode(10);
  
    puts("Created Linked List: ");
    printList(head);
    deleteLast(head, 2);
    puts("\nLinked List after Deletion of 1: ");
    printList(head);
    return 0;
}

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Java

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// A Java program to demonstrate deletion of last 
// Node in singly linked list 
class GFG
{
      
  
// A linked list Node 
static class Node 
    int key; 
    Node next; 
}; 
  
static Node deleteLast(Node head, int key) 
    // Initialize previous of Node to be deleted 
    Node x = null
  
    // Start from head and find the Node to be 
    // deleted 
    Node temp = head; 
    while (temp != null
    
        // If we found the key, update xv 
        if (temp.key == key) 
            x = temp; 
  
        temp = temp.next; 
    
  
    // key occurs at-least once 
    if (x != null
    
  
        // Copy key of next Node to x 
        x.key = x.next.key; 
  
        // Store and unlink next 
        temp = x.next; 
        x.next = x.next.next; 
  
        // Free memory for next 
    
    return head;
  
/// Utility function to create a new node with 
//given key /
static Node newNode(int key) 
    Node temp = new Node(); 
    temp.key = key; 
    temp.next = null
    return temp; 
  
// This function prints contents of linked list 
// starting from the given Node 
static void printList( Node node) 
    while (node != null
    
        System.out.printf(" %d ", node.key); 
        node = node.next; 
    
  
// Driver code/
public static void main(String args[])
    // /Start with the empty list /
    Node head = newNode(1); 
    head.next = newNode(2); 
    head.next.next = newNode(3); 
    head.next.next.next = newNode(5); 
    head.next.next.next.next = newNode(2); 
    head.next.next.next.next.next = newNode(10); 
  
    System.out.printf("Created Linked List: "); 
    printList(head); 
    deleteLast(head, 2); 
    System.out.printf("\nLinked List after Deletion of 1: "); 
    printList(head); 
}
  
// This code is contributed by Arnab Kundu

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C#

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// C# program to demonstrate deletion of last 
// Node in singly linked list 
using System;
  
class GFG 
      
  
// A linked list Node 
public class Node 
    public int key; 
    public Node next; 
}; 
  
static Node deleteLast(Node head, int key) 
    // Initialize previous of Node to be deleted 
    Node x = null
  
    // Start from head and find the Node to be 
    // deleted 
    Node temp = head; 
    while (temp != null
    
        // If we found the key, update xv 
        if (temp.key == key) 
            x = temp; 
  
        temp = temp.next; 
    
  
    // key occurs at-least once 
    if (x != null
    
  
        // Copy key of next Node to x 
        x.key = x.next.key; 
  
        // Store and unlink next 
        temp = x.next; 
        x.next = x.next.next; 
  
        // Free memory for next 
    
    return head; 
  
/// Utility function to create a new node with 
//given key / 
static Node newNode(int key) 
    Node temp = new Node(); 
    temp.key = key; 
    temp.next = null
    return temp; 
  
// This function prints contents of linked list 
// starting from the given Node 
static void printList( Node node) 
    while (node != null
    
        Console.Write(" {0} ", node.key); 
        node = node.next; 
    
  
// Driver code/ 
public static void Main(String []args) 
    // /Start with the empty list / 
    Node head = newNode(1); 
    head.next = newNode(2); 
    head.next.next = newNode(3); 
    head.next.next.next = newNode(5); 
    head.next.next.next.next = newNode(2); 
    head.next.next.next.next.next = newNode(10); 
  
    Console.Write("Created Linked List: "); 
    printList(head); 
    deleteLast(head, 2); 
    Console.Write("\nLinked List after Deletion of 1: "); 
    printList(head); 
  
// This code has been contributed by 29AjayKumar

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Output:

Created Linked List: 
 1  2  3  5  2  10 
Linked List after Deletion of 1: 
 1  2  3  5  10

The above solution doesn’t work when the node to be deleted is the last node.

Following solution handles all cases.

C++

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// A C program to demonstrate deletion of last
// Node in singly linked list
#include <stdio.h>
#include <stdlib.h>
  
// A linked list Node
struct Node {
    int data;
    struct Node* next;
};
  
// Function to delete the last occurrence
void deleteLast(struct Node* head, int x)
{
    struct Node *temp = head, *ptr = NULL;
    while (temp) {
  
        // If found key, update
        if (temp->data == x) 
            ptr = temp;        
        temp = temp->next;
    }
  
    // If the last occurrence is the last node
    if (ptr != NULL && ptr->next == NULL) {
        temp = head;
        while (temp->next != ptr) 
            temp = temp->next;       
        temp->next = NULL;
    }
  
    // If it is not the last node
    if (ptr != NULL && ptr->next != NULL) {
        ptr->data = ptr->next->data;
        temp = ptr->next;
        ptr->next = ptr->next->next;
        free(temp);
    }
}
  
/* Utility function to create a new node with
given key */
struct Node* newNode(int x)
{
    struct Node* node = malloc(sizeof(struct Node*));
    node->data = x;
    node->next = NULL;
    return node;
}
  
// This function prints contents of linked list
// starting from the given Node
void display(struct Node* head)
{
    struct Node* temp = head;
    if (head == NULL) {
        printf("NULL\n");
        return;
    }
    while (temp != NULL) {
        printf("%d --> ", temp->data);
        temp = temp->next;
    }
    printf("NULL\n");
}
  
/* Drier program to test above functions*/
int main()
{
    struct Node* head = newNode(1);
    head->next = newNode(2);
    head->next->next = newNode(3);
    head->next->next->next = newNode(4);
    head->next->next->next->next = newNode(5);
    head->next->next->next->next->next = newNode(4);
    head->next->next->next->next->next->next = newNode(4);
    printf("Created Linked list: ");
    display(head);
    deleteLast(head, 4);
    printf("List after deletion of 4: ");
    display(head);
    return 0;
}

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Java

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// Java program to demonstrate deletion of last 
// Node in singly linked list 
class GFG 
{
  
// A linked list Node 
static class Node 
    int data; 
    Node next; 
}; 
  
// Function to delete the last occurrence 
static void deleteLast(Node head, int x) 
    Node temp = head, ptr = null
    while (temp!=null
    
  
        // If found key, update 
        if (temp.data == x) 
            ptr = temp;     
        temp = temp.next; 
    
  
    // If the last occurrence is the last node 
    if (ptr != null && ptr.next == null
    
        temp = head; 
        while (temp.next != ptr) 
            temp = temp.next; 
        temp.next = null
    
  
    // If it is not the last node 
    if (ptr != null && ptr.next != null)
    
        ptr.data = ptr.next.data; 
        temp = ptr.next; 
        ptr.next = ptr.next.next; 
        System.gc();
    
  
/* Utility function to create a new node with 
given key */
static Node newNode(int x) 
    Node node = new Node(); 
    node.data = x; 
    node.next = null
    return node; 
  
// This function prints contents of linked list 
// starting from the given Node 
static void display(Node head) 
    Node temp = head; 
    if (head == null
    
        System.out.print("null\n"); 
        return
    
    while (temp != null
    
        System.out.printf("%d --> ", temp.data); 
        temp = temp.next; 
    
    System.out.print("null\n"); 
  
/* Driver code*/
public static void main(String[] args) 
{
    Node head = newNode(1); 
    head.next = newNode(2); 
    head.next.next = newNode(3); 
    head.next.next.next = newNode(4); 
    head.next.next.next.next = newNode(5); 
    head.next.next.next.next.next = newNode(4); 
    head.next.next.next.next.next.next = newNode(4); 
    System.out.print("Created Linked list: "); 
    display(head); 
    deleteLast(head, 4); 
    System.out.print("List after deletion of 4: "); 
    display(head); 
}
}
  
/* This code is contributed by PrinciRaj1992 */

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C#

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// C# program to demonstrate deletion of last 
// Node in singly linked list 
using System;
  
class GFG 
{
  
// A linked list Node 
public class Node 
    public int data; 
    public Node next; 
}; 
  
// Function to delete the last occurrence 
static void deleteLast(Node head, int x) 
    Node temp = head, ptr = null
    while (temp != null
    
  
        // If found key, update 
        if (temp.data == x) 
            ptr = temp;     
        temp = temp.next; 
    
  
    // If the last occurrence is the last node 
    if (ptr != null && ptr.next == null
    
        temp = head; 
        while (temp.next != ptr) 
            temp = temp.next; 
        temp.next = null
    
  
    // If it is not the last node 
    if (ptr != null && ptr.next != null)
    
        ptr.data = ptr.next.data; 
        temp = ptr.next; 
        ptr.next = ptr.next.next; 
    
  
/* Utility function to create a new node with 
given key */
static Node newNode(int x) 
    Node node = new Node(); 
    node.data = x; 
    node.next = null
    return node; 
  
// This function prints contents of linked list 
// starting from the given Node 
static void display(Node head) 
    Node temp = head; 
    if (head == null
    
        Console.Write("null\n"); 
        return
    
    while (temp != null
    
        Console.Write("{0} --> ", temp.data); 
        temp = temp.next; 
    
    Console.Write("null\n"); 
  
/* Driver code*/
public static void Main(String[] args) 
{
    Node head = newNode(1); 
    head.next = newNode(2); 
    head.next.next = newNode(3); 
    head.next.next.next = newNode(4); 
    head.next.next.next.next = newNode(5); 
    head.next.next.next.next.next = newNode(4); 
    head.next.next.next.next.next.next = newNode(4); 
    Console.Write("Created Linked list: "); 
    display(head); 
    deleteLast(head, 4); 
    Console.Write("List after deletion of 4: "); 
    display(head); 
}
}
  
// This code contributed by Rajput-Ji

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Output:

Created Linked List: 
 1  2  3  4  5  4  4 
Linked List after Deletion of 1: 
 1  2  3  4  5  4

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