Skip to content
Related Articles

Related Articles

Improve Article
Save Article
Like Article

Sort the biotonic doubly linked list | Set-2

  • Difficulty Level : Easy
  • Last Updated : 24 Jun, 2021

Sort the given biotonic doubly linked list. A biotonic doubly linked list is a doubly-linked list which is first increasing and then decreasing. A strictly increasing or a strictly decreasing list is also a biotonic doubly linked list. 
Examples: 
 

Input : 2 5 7 12 10 6 4 1
Output : 1 2 4 5 6 7 10 12

Input : 20 17 14 8 3
Output : 3 8 14 17 20

 

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.  To complete your preparation from learning a language to DS Algo and many more,  please refer Complete Interview Preparation Course.

In case you wish to attend live classes with experts, please refer DSA Live Classes for Working Professionals and Competitive Programming Live for Students.

In the previous post, we split the bitonic doubly linked list, reverse the second half and then merge both halves. In this post, another alternative method is discussed. The idea is to maintain two pointers, one pointing to head element initially and other pointing to the last element of a doubly linked list. Compare both the elements and add the smaller element to result in a list. The advance pointer of that element to the next adjacent element. Repeat this until all elements of input doubly linked list are added to result in the list.
Below is the implementation of above algorithm: 
 

C++




// C++ implementation to sort the biotonic
// doubly linked list
 
#include <bits/stdc++.h>
using namespace std;
 
// structure of node of the doubly linked list
struct Node {
    int data;
    struct Node* next;
    struct Node* prev;
};
 
// function to sort a biotonic doubly linked list
struct Node* sort(struct Node* head)
{
    // If number of elements are less than or
    // equal to 1 then return.
    if (head == NULL || head->next == NULL) {
        return head;
    }
 
    // Pointer to first element of doubly
    // linked list.
    Node* front = head;
 
    // Pointer to last element of doubly
    // linked list.
    Node* last = head;
 
    // Dummy node to which resultant
    // sorted list is added.
    Node* res = new Node;
 
    // Node after which next element
    // of sorted list is added.
    Node* resEnd = res;
 
    // Node to store next element to
    // which pointer is moved after
    // element pointed by that pointer
    // is added to result list.
    Node* next;
 
    // Find last element of input list.
    while (last->next != NULL) {
        last = last->next;
    }
 
    // Compare first and last element
    // until both pointers are not equal.
    while (front != last) {
 
        // If last element data is less than
        // or equal to front element data,
        // then add last element to
        // result list and change the
        // last pointer to its previous
        // element.
        if (last->data <= front->data) {
            resEnd->next = last;
            next = last->prev;
            last->prev->next = NULL;
            last->prev = resEnd;
            last = next;
            resEnd = resEnd->next;
        }
 
        // If front element is smaller, then
        // add it to result list and change
        // front pointer to its next element.
        else {
            resEnd->next = front;
            next = front->next;
            front->next = NULL;
            front->prev = resEnd;
            front = next;
            resEnd = resEnd->next;
        }
    }
 
    // Add the single element left to the
    // result list.
    resEnd->next = front;
    front->prev = resEnd;
 
    // The head of required sorted list is
    // next to dummy node res.
    return res->next;
}
 
// Function to insert a node at the beginning
// of the Doubly Linked List
void push(struct Node** head_ref, int new_data)
{
    // allocate node
    struct Node* new_node = (struct Node*)malloc(sizeof(struct Node));
 
    // put in the data
    new_node->data = new_data;
 
    // since we are adding at the beginning,
    // prev is always NULL
    new_node->prev = NULL;
 
    // link the old list off the new node
    new_node->next = (*head_ref);
 
    // change prev of head node to new node
    if ((*head_ref) != NULL)
        (*head_ref)->prev = new_node;
 
    // move the head to point to the new node
    (*head_ref) = new_node;
}
 
// Function to print nodes in a given doubly
// linked list
void printList(struct Node* head)
{
    // if list is empty
    if (head == NULL)
        cout << "Doubly Linked list empty";
 
    while (head != NULL) {
        cout << head->data << " ";
        head = head->next;
    }
}
 
// Driver program to test above
int main()
{
    struct Node* head = NULL;
 
    // Create the doubly linked list:
    // 2<->5<->7<->12<->10<->6<->4<->1
    push(&head, 1);
    push(&head, 4);
    push(&head, 6);
    push(&head, 10);
    push(&head, 12);
    push(&head, 7);
    push(&head, 5);
    push(&head, 2);
 
    cout << "Original Doubly linked list:\n";
    printList(head);
 
    // sort the biotonic DLL
    head = sort(head);
 
    cout << "\nDoubly linked list after sorting:\n";
    printList(head);
 
    return 0;
}


Java




// Java implementation to sort the biotonic
// doubly linked list
class GFG
{
     
// structure of node of the doubly linked list
static class Node
{
    int data;
    Node next;
    Node prev;
};
 
// function to sort a biotonic doubly linked list
static Node sort(Node head)
{
    // If number of elements are less than or
    // equal to 1 then return.
    if (head == null || head.next == null)
    {
        return head;
    }
 
    // Pointer to first element of doubly
    // linked list.
    Node front = head;
 
    // Pointer to last element of doubly
    // linked list.
    Node last = head;
 
    // Dummy node to which resultant
    // sorted list is added.
    Node res = new Node();
 
    // Node after which next element
    // of sorted list is added.
    Node resEnd = res;
 
    // Node to store next element to
    // which pointer is moved after
    // element pointed by that pointer
    // is added to result list.
    Node next;
 
    // Find last element of input list.
    while (last.next != null)
    {
        last = last.next;
    }
 
    // Compare first and last element
    // until both pointers are not equal.
    while (front != last)
    {
 
        // If last element data is less than
        // or equal to front element data,
        // then add last element to
        // result list and change the
        // last pointer to its previous
        // element.
        if (last.data <= front.data)
        {
            resEnd.next = last;
            next = last.prev;
            last.prev.next = null;
            last.prev = resEnd;
            last = next;
            resEnd = resEnd.next;
        }
 
        // If front element is smaller, then
        // add it to result list and change
        // front pointer to its next element.
        else
        {
            resEnd.next = front;
            next = front.next;
            front.next = null;
            front.prev = resEnd;
            front = next;
            resEnd = resEnd.next;
        }
    }
 
    // Add the single element left to the
    // result list.
    resEnd.next = front;
    front.prev = resEnd;
 
    // The head of required sorted list is
    // next to dummy node res.
    return res.next;
}
 
// Function to insert a node at the beginning
// of the Doubly Linked List
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;
 
    // since we are adding at the beginning,
    // prev is always null
    new_node.prev = null;
 
    // link the old list off the new node
    new_node.next = (head_ref);
 
    // change prev of head node to new node
    if ((head_ref) != null)
        (head_ref).prev = new_node;
 
    // move the head to point to the new node
    (head_ref) = new_node;
    return head_ref;
}
 
// Function to print nodes in a given doubly
// linked list
static void printList(Node head)
{
    // if list is empty
    if (head == null)
        System.out.print( "Doubly Linked list empty");
 
    while (head != null)
    {
        System.out.print( head.data + " ");
        head = head.next;
    }
}
 
// Driver code
public static void main(String args[])
{
    Node head = null;
 
    // Create the doubly linked list:
    // 2<.5<.7<.12<.10<.6<.4<.1
    head = push(head, 1);
    head = push(head, 4);
    head = push(head, 6);
    head = push(head, 10);
    head = push(head, 12);
    head = push(head, 7);
    head = push(head, 5);
    head = push(head, 2);
 
    System.out.print("Original Doubly linked list:\n");
    printList(head);
 
    // sort the biotonic DLL
    head = sort(head);
 
    System.out.print("\nDoubly linked list after sorting:\n");
    printList(head);
}
}
 
// This code is contributed by Arnab Kundu


Python3




# Python3 implementation to sort
# the biotonic doubly linked list
 
# structure of node of the doubly linked list
class Node: 
     
    def __init__(self, data):
        self.data = data
        self.prev = None
        self.next = None
  
# function to sort a biotonic doubly linked list
def sort(head):
  
    # If number of elements are less
    # than or equal to 1 then return.
    if head == None or head.next == None
        return head
 
    # Pointer to first element
    # of doubly linked list.
    front = head
 
    # Pointer to last element
    # of doubly linked list.
    last = head
 
    # Dummy node to which resultant
    # sorted list is added.
    res = Node(None)
 
    # Node after which next element
    # of sorted list is added.
    resEnd = res
 
    # Find last element of input list.
    while last.next != None:
        last = last.next
      
    # Compare first and last element
    # until both pointers are not equal.
    while front != last: 
 
        # If last element data is less than
        # or equal to front element data,
        # then add last element to
        # result list and change the last
        # pointer to its previous element.
        if last.data <= front.data:
            resEnd.next = last
            next = last.prev
            last.prev.next = None
            last.prev = resEnd
            last = next
            resEnd = resEnd.next
          
        # If front element is smaller, then
        # add it to result list and change
        # front pointer to its next element.
        else
            resEnd.next = front
            next = front.next
            front.next = None
            front.prev = resEnd
            front = next
            resEnd = resEnd.next
 
    # Add the single element left to the
    # result list.
    resEnd.next = front
    front.prev = resEnd
 
    # The head of required sorted list is
    # next to dummy node res.
    return res.next
  
# Function to insert a node at the
# beginning of the Doubly Linked List
def push(head_ref, new_data):
  
    # put in the data
    new_node = Node(new_data)
 
    # since we are adding at the
    # beginning, prev is always None
    new_node.prev = None
 
    # link the old list off the new node
    new_node.next = head_ref
 
    # change prev of head node to new node
    if head_ref != None:
        head_ref.prev = new_node
 
    # move the head to point to the new node
    head_ref = new_node
    return head_ref
 
# Function to print nodes in
# a given doubly linked list
def printList(head):
  
    # If list is empty
    if head == None:
        print("Doubly Linked list empty")
 
    while head != None
        print(head.data, end = " ")
        head = head.next
 
# Driver program to test above
if __name__ == '__main__':
  
    head = None
 
    # Create the doubly linked list:
    # 2<.5<.7<.12<.10<.6<.4<.1
    head = push(head, 1)
    head = push(head, 4)
    head = push(head, 6)
    head = push(head, 10)
    head = push(head, 12)
    head = push(head, 7)
    head = push(head, 5)
    head = push(head, 2)
 
    print("Original Doubly linked list:")
    printList(head)
 
    # sort the biotonic DLL
    head = sort(head)
 
    print("\nDoubly linked list after sorting:")
    printList(head)
         
# This code is contributed by Rituraj Jain


C#




// C# implementation to sort the biotonic
// doubly linked list
using System;
 
class GFG
{
     
// structure of node of the doubly linked list
public class Node
{
    public int data;
    public Node next;
    public Node prev;
};
 
// function to sort a biotonic doubly linked list
static Node sort(Node head)
{
    // If number of elements are less than or
    // equal to 1 then return.
    if (head == null || head.next == null)
    {
        return head;
    }
 
    // Pointer to first element of doubly
    // linked list.
    Node front = head;
 
    // Pointer to last element of doubly
    // linked list.
    Node last = head;
 
    // Dummy node to which resultant
    // sorted list is added.
    Node res = new Node();
 
    // Node after which next element
    // of sorted list is added.
    Node resEnd = res;
 
    // Node to store next element to
    // which pointer is moved after
    // element pointed by that pointer
    // is added to result list.
    Node next;
 
    // Find last element of input list.
    while (last.next != null)
    {
        last = last.next;
    }
 
    // Compare first and last element
    // until both pointers are not equal.
    while (front != last)
    {
 
        // If last element data is less than
        // or equal to front element data,
        // then add last element to
        // result list and change the
        // last pointer to its previous
        // element.
        if (last.data <= front.data)
        {
            resEnd.next = last;
            next = last.prev;
            last.prev.next = null;
            last.prev = resEnd;
            last = next;
            resEnd = resEnd.next;
        }
 
        // If front element is smaller, then
        // add it to result list and change
        // front pointer to its next element.
        else
        {
            resEnd.next = front;
            next = front.next;
            front.next = null;
            front.prev = resEnd;
            front = next;
            resEnd = resEnd.next;
        }
    }
 
    // Add the single element left to the
    // result list.
    resEnd.next = front;
    front.prev = resEnd;
 
    // The head of required sorted list is
    // next to dummy node res.
    return res.next;
}
 
// Function to insert a node at the beginning
// of the Doubly Linked List
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;
 
    // since we are adding at the beginning,
    // prev is always null
    new_node.prev = null;
 
    // link the old list off the new node
    new_node.next = (head_ref);
 
    // change prev of head node to new node
    if ((head_ref) != null)
        (head_ref).prev = new_node;
 
    // move the head to point to the new node
    (head_ref) = new_node;
    return head_ref;
}
 
// Function to print nodes in a given doubly
// linked list
static void printList(Node head)
{
    // if list is empty
    if (head == null)
        Console.Write( "Doubly Linked list empty");
 
    while (head != null)
    {
        Console.Write( head.data + " ");
        head = head.next;
    }
}
 
// Driver code
public static void Main(String []args)
{
    Node head = null;
 
    // Create the doubly linked list:
    // 2<.5<.7<.12<.10<.6<.4<.1
    head = push(head, 1);
    head = push(head, 4);
    head = push(head, 6);
    head = push(head, 10);
    head = push(head, 12);
    head = push(head, 7);
    head = push(head, 5);
    head = push(head, 2);
 
    Console.Write("Original Doubly linked list:\n");
    printList(head);
 
    // sort the biotonic DLL
    head = sort(head);
 
    Console.Write("\nDoubly linked list after sorting:\n");
    printList(head);
}
}
 
// This code contributed by Rajput-Ji


Javascript




<script>
 
      // JavaScript implementation to sort the biotonic
      // doubly linked list
      // structure of node of the doubly linked list
      class Node {
        constructor() {
          this.data = 0;
          this.next = null;
          this.prev = null;
        }
      }
 
      // function to sort a biotonic doubly linked list
      function sort(head) {
        // If number of elements are less than or
        // equal to 1 then return.
        if (head == null || head.next == null) {
          return head;
        }
 
        // Pointer to first element of doubly
        // linked list.
        var front = head;
 
        // Pointer to last element of doubly
        // linked list.
        var last = head;
 
        // Dummy node to which resultant
        // sorted list is added.
        var res = new Node();
 
        // Node after which next element
        // of sorted list is added.
        var resEnd = res;
 
        // Node to store next element to
        // which pointer is moved after
        // element pointed by that pointer
        // is added to result list.
        var next;
 
        // Find last element of input list.
        while (last.next != null) {
          last = last.next;
        }
 
        // Compare first and last element
        // until both pointers are not equal.
        while (front != last) {
          // If last element data is less than
          // or equal to front element data,
          // then add last element to
          // result list and change the
          // last pointer to its previous
          // element.
          if (last.data <= front.data) {
            resEnd.next = last;
            next = last.prev;
            last.prev.next = null;
            last.prev = resEnd;
            last = next;
            resEnd = resEnd.next;
          }
 
          // If front element is smaller, then
          // add it to result list and change
          // front pointer to its next element.
          else {
            resEnd.next = front;
            next = front.next;
            front.next = null;
            front.prev = resEnd;
            front = next;
            resEnd = resEnd.next;
          }
        }
 
        // Add the single element left to the
        // result list.
        resEnd.next = front;
        front.prev = resEnd;
 
        // The head of required sorted list is
        // next to dummy node res.
        return res.next;
      }
 
      // Function to insert a node at the beginning
      // of the Doubly Linked List
      function push(head_ref, new_data) {
        // allocate node
        var new_node = new Node();
 
        // put in the data
        new_node.data = new_data;
 
        // since we are adding at the beginning,
        // prev is always null
        new_node.prev = null;
 
        // link the old list off the new node
        new_node.next = head_ref;
 
        // change prev of head node to new node
        if (head_ref != null) head_ref.prev = new_node;
 
        // move the head to point to the new node
        head_ref = new_node;
        return head_ref;
      }
 
      // Function to print nodes in a given doubly
      // linked list
      function printList(head) {
        // if list is empty
        if (head == null) document.write("Doubly Linked list empty");
 
        while (head != null) {
          document.write(head.data + " ");
          head = head.next;
        }
      }
 
      // Driver code
      var head = null;
 
      // Create the doubly linked list:
      // 2<.5<.7<.12<.10<.6<.4<.1
      head = push(head, 1);
      head = push(head, 4);
      head = push(head, 6);
      head = push(head, 10);
      head = push(head, 12);
      head = push(head, 7);
      head = push(head, 5);
      head = push(head, 2);
 
      document.write("Original Doubly linked list: <br>");
      printList(head);
 
      // sort the biotonic DLL
      head = sort(head);
 
      document.write("<br>Doubly linked list after sorting:<br>");
      printList(head);
       
</script>


Output:  

Original Doubly linked list:
2 5 7 12 10 6 4 1
Doubly linked list after sorting:
1 2 4 5 6 7 10 12 

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




My Personal Notes arrow_drop_up
Recommended Articles
Page :

Start Your Coding Journey Now!