We have discussed Insertion Sort for arrays. In this article we are going to discuss Insertion Sort for linked list.
Below is a simple insertion sort algorithm for a linked list.
1) Create an empty sorted (or result) list. 2) Traverse the given list, do following for every node. ......a) Insert current node in sorted way in sorted or result list. 3) Change head of given linked list to head of sorted (or result) list.
The main step is (2.a) which has been covered in the post Sorted Insert for Singly Linked List Below is implementation of above algorithm:
Python
# Python implementation of above # algorithm# Node class class Node: # Constructor to initialize the # node object def __init__(self, data): self.data = data self.next = None# Function to sort a singly # linked list using insertion # sortdef insertionSort(head_ref): # Initialize sorted linked list sorted = None # Traverse the given linked list # and insert every node to sorted current = head_ref while (current != None): # Store next for next iteration next = current.next # Insert current in sorted # linked list sorted = sortedInsert(sorted, current) # Update current current = next # Update head_ref to point to # sorted linked list head_ref = sorted return head_ref# Function to insert a new_node in a list. # Note that this function expects a pointer # to head_ref as this can modify the head # of the input linked list (similar to push())def sortedInsert(head_ref, new_node): current = None # Special case for the head end if (head_ref == None or (head_ref).data >= new_node.data): new_node.next = head_ref head_ref = new_node else: # Locate the node before the point # of insertion current = head_ref while (current.next != None and current.next.data < new_node.data): current = current.next new_node.next = current.next current.next = new_node return head_ref# Utility Functions# Function to print linked listdef printList(head): temp = head while(temp != None): print( temp.data, end = " ") temp = temp.next # A utility function to insert a node# at the beginning of linked list def push( head_ref, new_data): # Allocate node new_node = Node(0) # 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 codea = Nonea = push(a, 5)a = push(a, 20)a = push(a, 4)a = push(a, 3)a = push(a, 30)print("Linked List before sorting ")printList(a)a = insertionSort(a)print("Linked List after sorting ")printList(a)# This code is contributed by Arnab Kundu |
Java
// Java implementation of the above algorithm// Node classclass Node { int data; Node next; // Constructor to initialize the node object public Node(int data) { this.data = data; this.next = null; }}public class InsertionSortLinkedList { // Function to sort a singly linked list using insertion // sort public static Node insertionSort(Node head) { // Initialize sorted linked list Node sorted = null; // Traverse the given linked list and insert every // node to sorted Node current = head; while (current != null) { // Store next for next iteration Node next = current.next; // Insert current in sorted linked list sorted = sortedInsert(sorted, current); // Update current current = next; } // Return head_ref to point to sorted linked list return sorted; } // Function to insert a new_node in a list. // Note that this function expects a pointer to head_ref // as this can modify the head of the input linked list // (similar to push()) public static Node sortedInsert(Node head, Node new_node) { Node current = null; // Special case for the head end if (head == null || head.data >= new_node.data) { new_node.next = head; head = new_node; } else { // Locate the node before the point of insertion current = head; while (current.next != null && current.next.data < new_node.data) { current = current.next; } new_node.next = current.next; current.next = new_node; } return head; } // Utility Functions // Function to print linked list public static void printList(Node head) { Node temp = head; while (temp != null) { System.out.print(temp.data + " "); temp = temp.next; } } // A utility function to insert a node at the beginning // of linked list public static Node push(Node head, int new_data) { // Allocate node Node new_node = new Node(new_data); // Link the old list of the new node new_node.next = head; // Move the head to point to the new node head = new_node; return head; } // Driver code public static void main(String[] args) { Node a = null; a = push(a, 5); a = push(a, 20); a = push(a, 4); a = push(a, 3); a = push(a, 30); System.out.println("Linked List before sorting "); printList(a); a = insertionSort(a); System.out.println("\nLinked List after sorting "); printList(a); }} |
Output:
Linked List before sorting 30 3 4 20 5 Linked List after sorting 3 4 5 20 30
Time Complexity: O(n2), in the worst case, we might have to traverse all nodes of the sorted list for inserting a node, and there are “n” such nodes.
Auxiliary Space : O(1), no extra space is required depending on the size of the input, thus it is constant.
Please refer complete article on Insertion Sort for Singly Linked List for more details!
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