C Exercises: Remove elements with odd indices from a linked list

Last update on March 19 2025 12:38:24 (UTC/GMT +8 hours)

25. Odd Index Removal Challenges

Write a C program that removes elements with odd indices from a singly linked list.

Sample Solution:

C Code:

#include<stdio.h>
#include <stdlib.h>

// Definition for singly-linked list.
struct Node {
    int data;
    struct Node* next;
};

// Function to remove elements with odd indices from a linked list
void removeOddIndices(struct Node** head) {
    struct Node* current = *head;  // Pointer to traverse the list
    struct Node* prev = NULL;      // Pointer to track the previous node
    int count = 1;                 // Variable to track the index of nodes, starting from 1

    while (current != NULL) { // Iterate through the linked list
        if (count % 2 == 1) { // Check if the index is odd
            if (prev == NULL) { // If the current node is the head
                *head = current->next; // Update head to the next node
            } else {
                prev->next = current->next; // Skip the current node by adjusting pointers
            }
            struct Node* temp = current; // Store the current node to free it later
            current = current->next; // Move to the next node
            free(temp); // Free the memory of the removed node
        } else {
            prev = current; // Move the 'prev' pointer to the current node
            current = current->next; // Move to the next node
        }
        count++; // Increment the index count
    }
}

// Function to insert a new node at the beginning of the linked list
void push(struct Node** head, int data) {
    struct Node* new_node = (struct Node*)malloc(sizeof(struct Node)); // Allocate memory for a new node
    new_node->data = data; // Assign data to the new node
    new_node->next = *head; // Set the next of the new node to the current head
    *head = new_node; // Update the head to point to the new node
}

// Function to print the linked list
void printList(struct Node* head) {
    while (head != NULL) { // Iterate through the linked list
        printf("%d ", head->data); // Print the data of the current node
        head = head->next; // Move to the next node
    }
    printf("\n"); // Print a new line after printing all nodes
}

// Test function to demonstrate the removal of odd-indexed elements
int main() {
    struct Node* head = NULL; // Initialize an empty linked list

    // Create a linked list with some initial values
    push(&head, 1);
    push(&head, 2);
    push(&head, 3);
    push(&head, 4);
    push(&head, 5);
    push(&head, 6);
    push(&head, 7);

    printf("Original linked list:\n");
    printList(head); // Display the original linked list
    removeOddIndices(&head); // Call function to remove odd-indexed elements
    printf("\nLinked list after removing odd indices:\n");
    printList(head); // Display the modified linked list after removal
    printf("\n");
    return 0; // Indicate successful completion of the program
}

Sample Output:

Original linked list:
7 6 5 4 3 2 1

Linked list after removing odd indices:
6 4 2

Flowchart :

For more Practice: Solve these Related Problems:

Write a C program to delete nodes at odd indices recursively from a singly linked list.
Write a C program to remove nodes with odd indices only if their values are prime numbers.
Write a C program to remove nodes at odd positions using pointer arithmetic and without using extra memory.
Write a C program to remove nodes at odd indices and then reverse the remaining list in one pass.

C Programming Code Editor:

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