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Sort a Linked List of 0s and 1s

  • Difficulty Level : Basic
  • Last Updated : 01 Dec, 2021

Given the head of a Linked List of size N, consisting of binary integers 0s and 1s, the task is to sort the given linked list.

Examples:

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Input: head = 1 -> 0 -> 1 -> 0 -> 1 -> 0 -> NULL 
Output: 0 -> 0 -> 0 -> 1 -> 1 -> 1 -> NULL



Input: head = 1 -> 1 -> 0 -> NULL 
Output: 0 -> 1 -> 1 -> NULL

Naive Approach: The simplest approach to solve the given problem is to perform the merge sort or insertion sort on the given linked list and sort it. The Implementation of Sorting the Linked list using Merge sort and Sorting the linked list using Insertion sort is discussed already. 
Time complexity: O(N * log N)
Auxiliary Space: O(N)

Efficient Approach: The above approach can also be optimized by counting the number of 1s and 0s in the given linked list and update the value of nodes accordingly in the linked list. Follow the steps to solve the problem:

  • Traverse the given linked list and store the count of 0s and 1s in variables, say zeroes and ones respectively.
  • Now, traverse the linked list again and change the first zeroes nodes with value 0 and then the remaining nodes with the value 1.
  • After completing the above steps, print the linked list as the resultant sorted list.

Below is the implementation of the above approach:

C++




// C++ program for the above approach
 
#include <bits/stdc++.h>
using namespace std;
 
// Link list node
class Node {
public:
    int data;
    Node* next;
};
 
// Function to print linked list
void printList(Node* node)
{
    // Iterate until node is NOT NULL
    while (node != NULL) {
 
        // Print the data
        cout << node->data << " ";
        node = node->next;
    }
}
 
// Function to sort the linked list
// consisting of 0s and 1s
void sortList(Node* head)
{
    // Base Case
    if ((head == NULL)
        || (head->next == NULL)) {
        return;
    }
 
    // Store the count of 0s and 1s
    int count0 = 0, count1 = 0;
 
    // Stores the head node
    Node* temp = head;
 
    // Traverse the list Head
    while (temp != NULL) {
 
        // If node->data value is 0
        if (temp->data == 0) {
 
            // Increment count0 by 1
            count0++;
        }
 
        // Otherwise, increment the
        // count of 1s
        else {
            count1++;
        }
 
        // Update the temp node
        temp = temp->next;
    }
 
    // Update the temp to head
    temp = head;
 
    // Traverse the list and update
    // the first count0 nodes as 0
    while (count0--) {
        temp->data = 0;
        temp = temp->next;
    }
 
    // Now, update the value of the
    // remaining count1 nodes as 1
    while (count1--) {
        temp->data = 1;
        temp = temp->next;
    }
 
    // Print the Linked List
    printList(head);
}
 
// Function to push a node
void push(Node** head_ref, int new_data)
{
    // Allocate node
    Node* new_node = new Node();
 
    // Put in the data
    new_node->data = new_data;
 
    // Link the old list of the
    // new node
    new_node->next = (*head_ref);
 
    // Move the head to point to
    // the new node
    (*head_ref) = new_node;
}
 
// Driver Code
int main(void)
{
    Node* head = NULL;
    push(&head, 0);
    push(&head, 1);
    push(&head, 0);
    push(&head, 1);
    push(&head, 1);
    push(&head, 1);
    push(&head, 1);
    push(&head, 1);
    push(&head, 0);
    sortList(head);
 
    return 0;
}


Java




// Java program for the above approach
import java.util.*;
class GFG{
 
  // Link list node
  static class Node {
 
    int data;
    Node next;
  };
 
  // Function to print linked list
  static void printList(Node node)
  {
 
    // Iterate until node is NOT null
    while (node != null) {
 
      // Print the data
      System.out.print(node.data+ " ");
      node = node.next;
    }
  }
 
  // Function to sort the linked list
  // consisting of 0s and 1s
  static void sortList(Node head)
  {
    // Base Case
    if ((head == null)
        || (head.next == null)) {
      return;
    }
 
    // Store the count of 0s and 1s
    int count0 = 0, count1 = 0;
 
    // Stores the head node
    Node temp = head;
 
    // Traverse the list Head
    while (temp != null) {
 
      // If node.data value is 0
      if (temp.data == 0) {
 
        // Increment count0 by 1
        count0++;
      }
 
      // Otherwise, increment the
      // count of 1s
      else {
        count1++;
      }
 
      // Update the temp node
      temp = temp.next;
    }
 
    // Update the temp to head
    temp = head;
 
    // Traverse the list and update
    // the first count0 nodes as 0
    while (count0>0) {
      temp.data = 0;
      temp = temp.next;
      count0--;
    }
 
    // Now, update the value of the
    // remaining count1 nodes as 1
    while (count1>0) {
      temp.data = 1;
      temp = temp.next;
      count1--;
    }
 
    // Print the Linked List
    printList(head);
  }
 
  // Function to push a node
  static Node push(Node head_ref, int new_data)
  {
    // Allocate node
    Node new_node = new Node();
 
    // Put in the data
    new_node.data = new_data;
 
    // Link the old list of the
    // new node
    new_node.next = head_ref;
 
    // Move the head to point to
    // the new node
    head_ref = new_node;
    return head_ref;
  }
 
  // Driver Code
  public static void main(String[] args)
  {
    Node head = null;
    head = push(head, 0);
    head = push(head, 1);
    head = push(head, 0);
    head = push(head, 1);
    head = push(head, 1);
    head = push(head, 1);
    head = push(head, 1);
    head = push(head, 1);
    head = push(head, 0);
    sortList(head);
 
  }
}
 
// This code is contributed by umadevi9616


C#




// C# program for the above approach
using System;
 
public class GFG {
 
    // Link list node
public    class Node {
 
    public    int data;
    public    Node next;
    };
 
    // Function to print linked list
    static void printList(Node node) {
 
        // Iterate until node is NOT null
        while (node != null) {
 
            // Print the data
            Console.Write(node.data + " ");
            node = node.next;
        }
    }
 
    // Function to sort the linked list
    // consisting of 0s and 1s
    static void sortList(Node head) {
        // Base Case
        if ((head == null) || (head.next == null)) {
            return;
        }
 
        // Store the count of 0s and 1s
        int count0 = 0, count1 = 0;
 
        // Stores the head node
        Node temp = head;
 
        // Traverse the list Head
        while (temp != null) {
 
            // If node.data value is 0
            if (temp.data == 0) {
 
                // Increment count0 by 1
                count0++;
            }
 
            // Otherwise, increment the
            // count of 1s
            else {
                count1++;
            }
 
            // Update the temp node
            temp = temp.next;
        }
 
        // Update the temp to head
        temp = head;
 
        // Traverse the list and update
        // the first count0 nodes as 0
        while (count0 > 0) {
            temp.data = 0;
            temp = temp.next;
            count0--;
        }
 
        // Now, update the value of the
        // remaining count1 nodes as 1
        while (count1 > 0) {
            temp.data = 1;
            temp = temp.next;
            count1--;
        }
 
        // Print the Linked List
        printList(head);
    }
 
    // Function to push a node
    static Node push(Node head_ref, int new_data) {
        // Allocate node
        Node new_node = new Node();
 
        // Put in the data
        new_node.data = new_data;
 
        // Link the old list of the
        // new node
        new_node.next = head_ref;
 
        // Move the head to point to
        // the new node
        head_ref = new_node;
        return head_ref;
    }
 
    // Driver Code
    public static void Main(String[] args) {
        Node head = null;
        head = push(head, 0);
        head = push(head, 1);
        head = push(head, 0);
        head = push(head, 1);
        head = push(head, 1);
        head = push(head, 1);
        head = push(head, 1);
        head = push(head, 1);
        head = push(head, 0);
        sortList(head);
 
    }
}
 
// This code is contributed by umadevi9616


Javascript




<script>
// javascript program for the above approach
 
    // Link list node
class Node {
    constructor() {
        this.data = 0;
        this.next = null;
    }
}
 
    // Function to prvar linked list
    function printList(node) {
 
        // Iterate until node is NOT null
        while (node != null) {
 
            // Prvar the data
            document.write(node.data + " ");
            node = node.next;
        }
    }
 
    // Function to sort the linked list
    // consisting of 0s and 1s
    function sortList(head)
    {
     
        // Base Case
        if ((head == null) || (head.next == null)) {
            return;
        }
 
        // Store the count of 0s and 1s
        var count0 = 0, count1 = 0;
 
        // Stores the head node
        var temp = head;
 
        // Traverse the list Head
        while (temp != null) {
 
            // If node.data value is 0
            if (temp.data == 0) {
 
                // Increment count0 by 1
                count0++;
            }
 
            // Otherwise, increment the
            // count of 1s
            else {
                count1++;
            }
 
            // Update the temp node
            temp = temp.next;
        }
 
        // Update the temp to head
        temp = head;
 
        // Traverse the list and update
        // the first count0 nodes as 0
        while (count0 > 0) {
            temp.data = 0;
            temp = temp.next;
            count0--;
        }
 
        // Now, update the value of the
        // remaining count1 nodes as 1
        while (count1 > 0) {
            temp.data = 1;
            temp = temp.next;
            count1--;
        }
 
        // Prvar the Linked List
        printList(head);
    }
 
    // Function to push a node
    function push(head_ref , new_data)
    {
     
        // Allocate node
        var new_node = new Node();
 
        // Put in the data
        new_node.data = new_data;
 
        // Link the old list of the
        // new node
        new_node.next = head_ref;
 
        // Move the head to povar to
        // the new node
        head_ref = new_node;
        return head_ref;
    }
 
    // Driver Code   
        var head = null;
        head = push(head, 0);
        head = push(head, 1);
        head = push(head, 0);
        head = push(head, 1);
        head = push(head, 1);
        head = push(head, 1);
        head = push(head, 1);
        head = push(head, 1);
        head = push(head, 0);
        sortList(head);
         
// This code is contributed by umadevi9616
</script>


Output: 

0 0 0 1 1 1 1 1 1

 

Time Complexity: O(N)
Auxiliary Space: O(1)




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