C Exercises: Reorder even-numbered before odd in a singly linked list

Last update on March 19 2025 12:38:22 (UTC/GMT +8 hours)

30. Reordering by Parity Challenges

Write a C program to create and reorder a linked list placing all even-numbered nodes ahead of all odd-numbered nodes.

Sample Solution:

C Code:

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

// Structure defining a node in a singly linked list
struct Node {
    int data; // Data stored in the node
    struct Node* next; // Pointer to the next node
};

// Function to create a new node in the singly linked list
struct Node* newNode(int data) {
    struct Node* node = (struct Node*) malloc(sizeof(struct Node)); // Allocate memory for a new node
    node->data = data; // Assign data to the new node
    node->next = NULL; // Initialize the next pointer as NULL
    return node; // Return the new node
}

// Function to reorder a singly linked list placing all even-numbered nodes ahead of all odd-numbered nodes
struct Node* odd_Even_List(struct Node* head) {
    if (!head) return head; // If the list is empty or has only one element, return the list
    struct Node *odd = head, *even = head->next, *even_Head = even; // Initialize odd and even pointers
    while (even && even->next) {
        odd->next = even->next; // Point odd nodes to the next odd node
        odd = odd->next; // Move odd pointer
        even->next = odd->next; // Point even nodes to the next even node
        even = even->next; // Move even pointer
    }
    odd->next = even_Head; // Connect the odd nodes to the even nodes
    return head; // Return the reordered list
}

// Function to print a linked list
void displayList(struct Node* head) {
    while (head) {
        printf("%d ", head->data); // Print the data of the current node
        head = head->next; // Move to the next node
    }
    printf("\n");
}

// Main function
int main() {
    struct Node* head = newNode(1); // Create and populate a singly linked list
    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(6);
    printf("Original Singly List:\n");
    displayList(head); // Display the original list

    struct Node* result; // Reorder the linked list placing all even-numbered nodes ahead of all odd-numbered nodes
    result = odd_Even_List(head);
    printf("\nReorder the said linked list placing all even-numbered \nnodes ahead of all odd-numbered nodes:\n");
    displayList(result); // Display the reordered list

    return 0;
}

Sample Output:

Original Singly List:
1 2 3 4 5 6 

Reorder the said linked list placing all even-numbered 
nodes ahead of all odd-numbered nodes:
1 3 5 2 4 6

Flowchart :

For more Practice: Solve these Related Problems:

Write a C program to reorder a linked list to place nodes at even indices before nodes at odd indices.
Write a C program to reorder a linked list such that nodes with even values come before nodes with odd values.
Write a C program to interleave nodes from odd and even positions in a linked list recursively.
Write a C program to reorder a linked list by reversing the sublist of nodes at even positions and appending it to odd-index nodes.

C Programming Code Editor:

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