Program to Sort the Elements of the Doubly Linked List

Q. Program to sort the elements of the doubly linked list.

Explanation

In this program, we will create a doubly linked list and sort nodes of the list in ascending order.

Original List:

Program to sort the elements of the doubly linked list

Sorted List:

To accomplish this, we maintain two pointers: current and index. Initially, current point to head node and index will point to node next to current. Traverse through the list till current points to null, by comparing current's data with index's data. If the current's data is greater than the index's data, then swap data between them. In above example, current will initially point to 7, and the index will point to 1. Since, 7 is greater than 1, swap the data. Continue this process till the entire list is sorted in ascending order.

Algorithm

Define a Node class which represents a node in the list. It will have three properties: data, previous which will point to the previous node and next which will point to the next node.
Define another class for creating a doubly linked list, and it has two nodes: head and tail. Initially, head and tail will point to null.
addNode() will add node to the list:
1. It first checks whether the head is null, then it will insert the node as the head.
2. Both head and tail will point to a newly added node.
3. Head's previous pointer will point to null and tail's next pointer will point to null.
4. If the head is not null, the new node will be inserted at the end of the list such that new node's previous pointer will point to tail.
5. The new node will become the new tail. Tail's next pointer will point to null.
sortList() will sort nodes of the list in ascending order.
1. Define a node current which will point to head.
2. Define another node index which will point to node next to current.
3. Compare data of current and index node. If the current's data is greater than the index's data, then swap the data between them.
4. Current will point to current.next and index will point to index.next.
5. Continue this process till the entire list is sorted.
display() will show all the nodes present in the list.
1. Define a new node 'current' that will point to the head.
2. Print current.data till current points to null.
3. Current will point to the next node in the list in each iteration.

Solution

Python

#Represent a node of doubly linked list
class Node:
    def __init__(self,data):
        self.data = data;
        self.previous = None;
        self.next = None;
        
class SortList:
    #Represent the head and tail of the doubly linked list
    def __init__(self):
        self.head = None;
        self.tail = None;
        
    #addNode() will add a node to the list
    def addNode(self, data):
        #Create a new node
        newNode = Node(data);
        
        #If list is empty
        if(self.head == None):
            #Both head and tail will point to newNode
            self.head = self.tail = newNode;
            #head's previous will point to None
            self.head.previous = None;
            #tail's next will point to None, as it is the last node of the list
            self.tail.next = None;
        else:
            #newNode will be added after tail such that tail's next will point to newNode
            self.tail.next = newNode;
            #newNode's previous will point to tail
            newNode.previous = self.tail;
            #newNode will become new tail
            self.tail = newNode;
            #As it is last node, tail's next will point to None
            self.tail.next = None;
            
    #sortList() will sort the given list in ascending order
    def sortList(self):
        #Check whether list is empty
        if(self.head == None):
            return;
        else:
            #Current will point to head
            current = self.head
            while(current.next != None):
                #Index will point to node next to current
                index = current.next;
                while(index != None):
                    #If current's data is greater than index's data, swap the data of current and index
                    if(current.data > index.data):
                        temp = current.data;
                        current.data = index.data;
                        index.data = temp;
                    index = index.next
                current = current.next
                
    #display() will print out the nodes of the list
    def display(self):
        #Node current will point to head
        current = self.head;
        if(self.head == None):
            print("List is empty");
            return;
        while(current != None):
            #Prints each node by incrementing pointer.
            print(current.data),
            current = current.next;
            
        print();
        
dList = SortList();
#Add nodes to the list
dList.addNode(7);
dList.addNode(1);
dList.addNode(4);
dList.addNode(5);
dList.addNode(2);
 
#Displaying original list
print("Original list: ");
dList.display();
 
#Sorting list
dList.sortList();
 
#Displaying a sorted list

print("Sorted list: ");
dList.display();

Output:

Original list: 
7 1 4 5 2 
Sorted list: 
1 2 4 5 7

C

#include <stdio.h>
 
//Represent a node of the doubly linked list

struct node{
    int data;
    struct node *previous;
    struct node *next;
};    
 
//Represent the head and tail of the doubly linked list
struct node *head, *tail = NULL;
 
//addNode() will add a node to the list
void addNode(int data) {
    //Create a new node
    struct node *newNode = (struct node*)malloc(sizeof(struct node));
    newNode->data = data;
    
    //If list is empty
    if(head == NULL) {
        //Both head and tail will point to newNode
        head = tail = newNode;
        //head's previous will point to NULL
        head->previous = NULL;
        //tail's next will point to NULL, as it is the last node of the list
        tail->next = NULL;
    }
    else {
        //newNode will be added after tail such that tail's next will point to newNode
        tail->next = newNode;
        //newNode's previous will point to tail
        newNode->previous = tail;
        //newNode will become new tail
        tail = newNode;
        //As it is last node, tail's next will point to NULL
        tail->next = NULL;
    }
}
 
//sortList() will sort the given list in ascending order
void sortList() {
    struct node *current = NULL, *index = NULL;
    int temp;
    //Check whether list is empty
    if(head == NULL) {
        return;
    }
    else {
        //Current will point to head
        for(current = head; current->next != NULL; current = current->next) {
            //Index will point to node next to current
            for(index = current->next; index != NULL; index = index->next) {
                //If current's data is greater than index's data, swap the data of current and index
                if(current->data > index->data) {
                    temp = current->data;
                    current->data = index->data;
                    index->data = temp;
                }
            }
        }
    }
}
 
//display() will print out the nodes of the list
void display() {
    //Node current will point to head
    struct node *current = head;
    if(head == NULL) {
        printf("List is empty\n");
        return;
    }
    while(current != NULL) {
        //Prints each node by incrementing pointer.
        printf("%d ",current->data);
        current = current->next;
    }
    printf("\n");
}
 
int main()
{
    //Add nodes to the list
    addNode(7);
    addNode(1);
    addNode(4);
    addNode(5);
    addNode(2);
    
    //Displaying original list
    printf("Original list: \n");
    display();
    
    //Sorting list
    sortList();
    
    //Displaying sorted list
    printf("Sorted list: \n");
    display();
 
    return 0;
}

Output:

Original list: 
7 1 4 5 2 
Sorted list: 
1 2 4 5 7

JAVA

public class SortList {
    
    //Represent a node of the doubly linked list

    class Node{
        int data;
        Node previous;
        Node next;
        
        public Node(int data) {
            this.data = data;
        }
    }
    
    //Represent the head and tail of the doubly linked list
    Node head, tail = null;
    
    //addNode() will add a node to the list
    public void addNode(int data) {
        //Create a new node
        Node newNode = new Node(data);
        
        //If list is empty
        if(head == null) {
            //Both head and tail will point to newNode
            head = tail = newNode;
            //head's previous will point to null
            head.previous = null;
            //tail's next will point to null, as it is the last node of the list
            tail.next = null;
        }
        else {
            //newNode will be added after tail such that tail's next will point to newNode
            tail.next = newNode;
            //newNode's previous will point to tail
            newNode.previous = tail;
            //newNode will become new tail
            tail = newNode;
            //As it is last node, tail's next will point to null
            tail.next = null;
        }
    }
    
    //sortList() will sort the given list in ascending order
    public void sortList() {
        Node current = null, index = null;
        int temp;
        //Check whether list is empty
        if(head == null) {
            return;
        }
        else {
            //Current will point to head
            for(current = head; current.next != null; current = current.next) {
                //Index will point to node next to current
                for(index = current.next; index != null; index = index.next) {
                    //If current's data is greater than index's data, swap the data of current and index
                    if(current.data > index.data) {
                        temp = current.data;
                        current.data = index.data;
                        index.data = temp;
                    }
                }
            }
        }
    }
    
    //display() will print out the nodes of the list
    public void display() {
        //Node current will point to head
        Node current = head;
        if(head == null) {
            System.out.println("List is empty");
            return;
        }
        while(current != null) {
            //Prints each node by incrementing the pointer.

            System.out.print(current.data + " ");
            current = current.next;
        }
        System.out.println();
    }
    
    public static void main(String[] args) {
        
        SortList dList = new SortList();
        //Add nodes to the list
        dList.addNode(7);
        dList.addNode(1);
        dList.addNode(4);
        dList.addNode(5);
        dList.addNode(2);
        
        //Displaying original list
        System.out.println("Original list: ");
        dList.display();
        
        //Sorting list
        dList.sortList();
        
        //Displaying sorted list
        System.out.println("Sorted list: ");
        dList.display();
    }
}

Output:

Original list: 
7 1 4 5 2 
Sorted list: 
1 2 4 5 7

C#

using System; 
namespace DoublyLinkedList 
{                     
    public class Program
    {
        //Represent a node of the doubly linked list

        public class Node<T>{
            public T data;
            public Node<T> previous;
            public Node<T> next;
            
            public Node(T value) {
                data = value;
            }
        }
        
        public class SortList<T> where T : IComparable<T>{
            //Represent the head and tail of the doubly linked list
            protected Node<T> head = null;             
             protected Node<T> tail = null;
            
            //addNode() will add a node to the list
            public void addNode(T data) {
                //Create a new node
                Node<T> newNode = new Node<T>(data);
 
                //If list is empty
                if(head == null) {
                    //Both head and tail will point to newNode
                    head = tail = newNode;
                    //head's previous will point to null
                    head.previous = null;
                    //tail's next will point to null, as it is the last node of the list
                    tail.next = null;
                }
                else {
                    //newNode will be added after tail such that tail's next will point to newNode
                    tail.next = newNode;
                    //newNode's previous will point to tail
                    newNode.previous = tail;
                    //newNode will become new tail
                    tail = newNode;
                    //As it is last node, tail's next will point to null
                    tail.next = null;
                }
            }
            
            //sortList() will sort the given list in ascending order
            public void sortList() {
                Node<T> current = null, index = null;
                T temp;
                //Check whether list is empty
                if(head == null) {
                    return;
                }
                else {
                    //Current will point to head
                    for(current = head; current.next != null; current = current.next) {
                        //Index will point to node next to current
                        for(index = current.next; index != null; index = index.next) {
                            //If current's data is greater than index's data, swap the data of current and index
                            if(current.data.CompareTo(index.data) > 0) {
                                temp = current.data;
                                current.data = index.data;
                                index.data = temp;
                            }
                        }
                    }
                }
            }
 
            //display() will print out the nodes of the list
            public void display() {
                //Node current will point to head
                Node<T> current = head;
                if(head == null) {
                    Console.WriteLine("List is empty");
                    return;
                }
                while(current != null) {
                    //Prints each node by incrementing the pointer.

                    Console.Write(current.data + " ");
                    current = current.next;
                }
                Console.WriteLine();
            }
 
        }
        
        public static void Main()
        {
            SortList<int> dList = new SortList<int>();
            //Add nodes to the list
            dList.addNode(7);
            dList.addNode(1);
            dList.addNode(4);
            dList.addNode(5);
            dList.addNode(2);
 
            //Displaying original list
            Console.WriteLine("Original list: ");
            dList.display();
 
            //Sorting list
            dList.sortList();
 
            //Displaying sorted list
            Console.WriteLine("Sorted list: ");
            dList.display();
        }    
    }
}

Output:

Original list: 
7 1 4 5 2 
Sorted list: 
1 2 4 5 7

PHP

<!DOCTYPE html>
<html>
<body>
<?php
//Represent a node of doubly linked list
class Node{
    public $data;
    public $previous;
    public $next;
    
    function __construct($data){
        $this->data = $data;
    }
}
class SortList{
    //Represent the head and tail of the doubly linked list
    public $head;
    public $tail;
    function __construct(){
        $this->head = NULL;
        $this->tail = NULL;
    }
    
    //addNode() will add a node to the list
    function addNode($data){
        //Create a new node
        $newNode = new Node($data);
        
        //If list is empty
        if($this->head == NULL) {
            //Both head and tail will point to newNode
            $this->head = $this->tail = $newNode;
            //head's previous will point to NULL
            $this->head->previous = NULL;
            //tail's next will point to NULL, as it is the last node of the list
            $this->tail->next = NULL;
        }
        else {
            //newNode will be added after tail such that tail's next will point to newNode
            $this->tail->next = $newNode;
            //newNode's previous will point to tail
            $newNode->previous = $this->tail;
            //newNode will become new tail
            $this->tail = $newNode;
            //As it is last node, tail's next will point to NULL
            $this->tail->next = NULL;
        }
    }
    
    //sortList() will sort the given list in ascending order
    function sortList() {
        //Check whether list is empty
        if($this->head == NULL) {
            return;
        }
        else {
            //Current will point to head
            for($current = $this->head; $current->next != NULL; $current = $current->next) {
                //Index will point to node next to current
                for($index = $current->next; $index != NULL; $index = $index->next) {
                    //If current's data is greater than index's data, swap the data of current and index
                    if($current->data > $index->data) {
                        $temp = $current->data;
                        $current->data = $index->data;
                        $index->data = $temp;
                    }
                }
            }
        }
    }
    
    //display() will print out the nodes of the list
    function display() {
        //Node current will point to head
        $current = $this->head;
        if($this->head == NULL) {
            print("List is empty <br>");
            return;
        }
        while($current != NULL) {
            //Prints each node by incrementing pointer.
            print($current->data . " ");
            $current = $current->next;
        }
        print("<br>");
    }
}
    
$dList = new SortList();
//Add nodes to the list
$dList->addNode(7);
$dList->addNode(1);
$dList->addNode(4);
$dList->addNode(5);
$dList->addNode(2);
 
//Displaying original list
print("Original list: <br>");
$dList->display();
 
//Sorting list
$dList->sortList();
 
//Displaying sorted list
print("Sorted list: <br>");
$dList->display();
?>
</body>
</html>

Output:

Original list: 
7 1 4 5 2 
Sorted list: 
1 2 4 5 7

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