C Exercises: Split a singly linked list into two halves

Last update on August 04 2025 13:01:08 (UTC/GMT +8 hours)

32. Halving the List Challenges

Write a C program to split a singly linked list into two halves.

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 *temp = (struct Node *)malloc(sizeof(struct Node)); // Allocate memory for a new node
    temp->data = data;  // Assign data to the new node
    temp->next = NULL;  // Initialize the next pointer as NULL
    return temp;  // Return the new node
}

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

// Function to split the singly linked list into two halves
void splitList(struct Node *head, struct Node **front_ref, struct Node **back_ref) {
    struct Node *slow = head;  // Initialize slow pointer to the head of the list
    struct Node *fast = head->next;  // Initialize fast pointer to the second node

    while (fast != NULL) {
        fast = fast->next;  // Move fast pointer by one step
        if (fast != NULL) {
            slow = slow->next;  // Move slow pointer by one step
            fast = fast->next;  // Move fast pointer by another step
        }
    }

    *front_ref = head;  // Set front_ref to the original head of the list
    *back_ref = slow->next;  // Set back_ref to the node next to the middle node
    slow->next = NULL;  // Break the link between the two halves
}

int main() {
    struct Node *temp;
    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);

    printf("Original List: ");
    printList(head);

    struct Node *firstHalf = NULL;
    struct Node *secondHalf = NULL;

    // Calling the splitList method for the first list
    splitList(head, &firstHalf, &secondHalf);
    printf("Split the said singly linked list into halves:\n");
    printf("First half: ");
    temp = firstHalf;
    printList(temp);
    printf("Second half: ");
    temp = secondHalf;
    printList(temp);

    // Creating a second list and performing the same splitting operation
    struct Node *head1 = newNode(1);
    head1->next = newNode(2);
    head1->next->next = newNode(3);
    head1->next->next->next = newNode(4);
    head1->next->next->next->next = newNode(5);
    head1->next->next->next->next->next = newNode(6);

    printf("\nOriginal List: ");
    printList(head1);

    firstHalf = NULL;
    secondHalf = NULL;

    // Calling the splitList method for the second list
    splitList(head1, &firstHalf, &secondHalf);
    printf("Split the said singly linked list into halves:\n");
    printf("First half: ");
    temp = firstHalf;
    printList(temp);
    printf("Second half: ");
    temp = secondHalf;
    printList(temp);

    return 0;
}

Sample Output:

Original List: 1 2 3 4 5 
Split the said singly linked list into halves:
First half: 1 2 3 
Second half: 4 5 

Original List: 1 2 3 4 5 6 
Split the said singly linked list into halves:
First half: 1 2 3 
Second half: 4 5 6

Flowchart :

For more Practice: Solve these Related Problems:

Write a C program to split a linked list into two halves, where the first half contains one more node if the total count is odd.
Write a C program to split a linked list into two halves by alternating nodes between the two lists.
Write a C program to split a linked list into two halves and then merge them back in alternating order.
Write a C program to split a linked list into two halves using the slow and fast pointer technique recursively.

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