C Program For Deleting Last Occurrence Of An Item From Linked List

Using pointers, loop through the whole list and keep track of the node prior to the node containing the last occurrence key using a special pointer. After this just store the next of next of the special pointer, into to next of special pointer to remove the required node from the linked list.

C

#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");
        return;
    }
    while (temp != NULL)
    {
        printf("%d --> ",
                temp->data);
        temp = temp->next;
    }
    printf("NULL");
}

// Driver code
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);

    // Pass the address of the head pointer
    deleteLast(&head, 4);
    printf("List after deletion of 4: ");
    display(head);
    return 0;
}

Output:

Created Linked list: 1 --> 2 --> 3 --> 4 --> 5 --> 4 --> 4 --> NULL
List after deletion of 4: 1 --> 2 --> 3 --> 4 --> 5 --> 4 --> NULL

Time Complexity: O(n) where n is the number of nodes in the given linked list.
Auxiliary Space: O(1), no extra space is required, so it is a constant.

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

C

// 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");
        return;
    }
    while (temp != NULL)
    {
        printf("%d --> ", temp->data);
        temp = temp->next;
    }
    printf("NULL");
}

// Driver code
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;
}

Output:

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

Time Complexity: O(n) where n is the number of nodes in the given linked list.
Auxiliary Space: O(1), no extra space is required, so it is a constant.

Please refer complete article on Delete last occurrence of an item from linked list for more details!