Python program to sort the elements of the Circular Linked List

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Python program to sort the elements of the Circular Linked List

In this program, we will create a circular linked list and sort the list in ascending order. In this example, we maintain two nodes: current which will point to head and index which will point to the next node to current. The first loop, keep track of current and second loop will keep track of index. In the first iteration, current will point to 9. The index will point to node next to the current which in this case is 5. 9 is compared with 5, since 9 > 5, swap data of index node with the current node. Now, the current will have 5. Now, 5 will be compared to 2. Again 5 > 2, swap the data. Now current will hold 2 and index will hold 7. 2 < 7, nothing will be done. The index will be incremented and pointed to 3.2< 3. Nothing will be done. In this way, we will have a minimum value node in the first position. Then, we will keep on finding minimum element in the rest of the list until the list is completely sorted.

  1. 9->5->2->7->3
  2. 2->9->5->7->3
  3. 2->3->9->7->5
  4. 2->3->5->9->7
  5. 2->3->5->7->9

ALGORITHM:

  1. Define a Node class which represents a node in the list. It has two properties data and next which will point to the next node.
  2. Define another class for creating a circular linked list, and it has two nodes: head and tail.
  3. sortList() will sort the list:
  • We will maintain two nodes current which points to head, and index will point to node next to current.
  • Traverse through the list starting from index till the end is reached.
  • If current.data is greater than the index.data, swap the data between them.
  • At the first iteration, we will get minimum element at the start of the list.
  • Then current will point to current.next.
  • Repeat steps b to e till we get next minimum node.
  • At the end of both the loop, the list will be sorted.

PROGRAM:

  1. #Represents the node of list.  
  2. class Node:
  3.     def __init__(self,data):
  4.         self.data = data;
  5.         self.next = None;
  6. class CreateList:
  7.     #Declaring head and tail pointer as null.  
  8.     def __init__(self):
  9.         self.head = Node(None);
  10.         self.tail = Node(None);
  11.         self.head.next = self.tail;
  12.         self.tail.next = self.head;
  13.     #This function will add the new node at the end of the list.  
  14.     def add(self,data):
  15.         newNode = Node(data);
  16.         #Checks if the list is empty.  
  17.         if self.head.data is None:
  18.             #If list is empty, both head and tail would point to new node.  
  19.             self.head = newNode;
  20.             self.tail = newNode;
  21.             newNode.next = self.head;
  22.         else:
  23.             #tail will point to new node.  
  24.             self.tail.next = newNode;
  25.             #New node will become new tail.  
  26.             self.tail = newNode;
  27.             #Since, it is circular linked list tail will point to head.  
  28.             self.tail.next = self.head;
  29.     #This function sorts the list in ascending order  
  30.     def sortList(self):
  31.         #Current will point to head  
  32.         current = self.head;
  33.         if(self.head == None):
  34.             print(“List is empty”);
  35.         else:
  36.             while(True):
  37.                 #Index will point to node next to current  
  38.                 index = current.next;
  39.                 while(index != self.head):
  40.                     #If current node is greater than index data, swaps the data  
  41.                     if(current.data > index.data):
  42.                         temp = current.data;
  43.                         current.data = index.data;
  44.                         index.data = temp;
  45.                     index= index.next;
  46.                 current =current.next;
  47.                 if(current.next == self.head):
  48.                     break;
  49.     #Displays all the nodes in the list  
  50.     def display(self):
  51.         current = self.head;
  52.         if self.head is None:
  53.             print(“List is empty”);
  54.             return;
  55.         else:
  56.             #Prints each node by incrementing pointer.  
  57.             print(current.data, end= ‘ ‘);
  58.             while(current.next != self.head):
  59.                 current = current.next;
  60.                 print(current.data,end=‘ ‘);
  61.         print(“\n”);
  62. class CircularLinkedList:
  63.     cl = CreateList();
  64.     #Adds data to the list  
  65.     cl.add(70);
  66.     cl.add(90);
  67.     cl.add(20);
  68.     cl.add(100);
  69.     cl.add(50);
  70.     #Displaying original list  
  71.     print(“Original list: “);
  72.     cl.display();
  73.     #Sorting list  
  74.     cl.sortList();
  75.     #Displaying sorted list  
  76.     print(“Sorted list: “);
  77.     cl.display();

Output:

Original list: 
70 90 20 100 50
Sorted list: 
20 50 70 90 100

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