C++ Program For Sorting A Linked List Of 0s, 1s And 2s By Changing Links

// C++ Program to sort a linked list 
// 0s, 1s or 2s by changing links
#include <bits/stdc++.h>

// Link list node 
struct Node 
{
    int data;
    struct Node* next;
};

Node* newNode(int data);

// Sort a linked list of 0s, 1s 
// and 2s by changing pointers.
Node* sortList(Node* head)
{
    if (!head || !(head->next))
        return head;

    // Create three dummy nodes to point 
    // to beginning of three linked lists. 
    // These dummy nodes are created to 
    // avoid many null checks.
    Node* zeroD = newNode(0);
    Node* oneD = newNode(0);
    Node* twoD = newNode(0);

    // Initialize current pointers for 
    // three lists and whole list.
    Node* zero = zeroD, *one = oneD, 
        *two = twoD;

    // Traverse list
    Node* curr = head;
    while (curr) 
    {
        if (curr->data == 0) 
        {
            zero->next = curr;
            zero = zero->next;
            curr = curr->next;
        }
        else if (curr->data == 1)
        {
            one->next = curr;
            one = one->next;
            curr = curr->next;
        }
        else 
        {
            two->next = curr;
            two = two->next;
            curr = curr->next;
        }
    }

    // Attach three lists
    zero->next = (oneD->next) ? 
                 (oneD->next) : (twoD->next);
    one->next = twoD->next;
    two->next = NULL;

    // Updated head
    head = zeroD->next;

    // Delete dummy nodes
    delete zeroD;
    delete oneD;
    delete twoD;

    return head;
}

// Function to create and return a node
Node* newNode(int data)
{
    // Allocating space
    Node* newNode = new Node;

    // Inserting the required data
    newNode->data = data;
    newNode->next = NULL;
}

// Function to print linked list 
void printList(struct Node* node)
{
    while (node != NULL)
    {
        printf("%d  ", node->data);
        node = node->next;
    }
    printf("");
}

// Driver code
int main(void)
{
    // Creating the list 1->2->4->5
    Node* head = newNode(1);
    head->next = newNode(2);
    head->next->next = newNode(0);
    head->next->next->next = newNode(1);

    printf("Linked List Before Sorting");
    printList(head);

    head = sortList(head);

    printf("Linked List After Sorting");
    printList(head);

    return 0;
}