Insertion Sort for Singly Linked List - GeeksforGeeks

25 Feb, 2022
We have discussed Insertion Sort for arrays. In this article, we are going to discuss Insertion Sort for a 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.
Recommended: Please try your approach on {IDE} first, before moving on to the solution
The main step is (2.a) which has been covered in the below post. Sorted Insert for Singly Linked List
Below is the implementation of the above algorithm
C
C++
Java
Python
C#
Javascript
// C program to sort link list// using insertion sort#include <stdio.h>#include <stdlib.h> struct node {    int data;    struct node* next;}; struct node* head = NULL;struct node* sorted = NULL; void push(int val){    /* allocate node */    struct node* newnode        = (struct node*)malloc(sizeof(struct node));    newnode->data = val;    /* link the old list off the new node */    newnode->next = head;    /* move the head to point to the new node */    head = newnode;} /* * 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()) */void sortedInsert(struct node* newnode){    /* Special case for the head end */    if (sorted == NULL || sorted->data >= newnode->data) {        newnode->next = sorted;        sorted = newnode;    }    else {        struct node* current = sorted;        /* Locate the node before the point of insertion         */        while (current->next != NULL               && current->next->data < newnode->data) {            current = current->next;        }        newnode->next = current->next;        current->next = newnode;    }} // function to sort a singly linked list// using insertion sortvoid insertionsort(){     struct node* current = head;     // Traverse the given linked list and insert every    // node to sorted    while (current != NULL) {         // Store next for next iteration        struct node* next = current->next;         // insert current in sorted linked list        sortedInsert(current);         // Update current        current = next;    }    // Update head to point to sorted linked list    head = sorted;} /* Function to print linked list */void printlist(struct node* head){    while (head != NULL) {        printf("%d->", head->data);        head = head->next;    }    printf("NULL");} // Driver program to test above functionsint main(){     push(5);    push(20);    push(4);    push(3);    push(30);     printf("Linked List before sorting:\n");    printlist(head);    printf("\n");     insertionsort(head);     printf("Linked List after sorting:\n");    printlist(head);} // This code is contributed by Sornodeep Chandra
// C++ program to sort link list// using insertion sort#include <bits/stdc++.h>using namespace std; struct Node {    int val;    struct Node* next;    Node(int x)    {        val = x;        next = NULL;    }}; class LinkedlistIS { public:    Node* head;    Node* sorted;     void push(int val)    {        /* allocate node */        Node* newnode = new Node(val);        /* link the old list off the new node */        newnode->next = head;        /* move the head to point to the new node */        head = newnode;    }     // function to sort a singly linked list using insertion    // sort    void insertionSort(Node* headref)    {        // Initialize sorted linked list        sorted = NULL;        Node* current = headref;        // Traverse the given linked list and insert every        // node to sorted        while (current != NULL) {            // Store next for next iteration            Node* next = current->next;            // insert current in sorted linked list            sortedInsert(current);            // Update current            current = next;        }        // Update head_ref to point to sorted linked list        head = 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())     */    void sortedInsert(Node* newnode)    {        /* Special case for the head end */        if (sorted == NULL || sorted->val >= newnode->val) {            newnode->next = sorted;            sorted = newnode;        }        else {            Node* current = sorted;            /* Locate the node before the point of insertion             */            while (current->next != NULL                   && current->next->val < newnode->val) {                current = current->next;            }            newnode->next = current->next;            current->next = newnode;        }    }    /* Function to print linked list */    void printlist(Node* head)    {        while (head != NULL) {            cout << head->val << " ";            head = head->next;        }    }};// Driver program to test above functionsint main(){    LinkedlistIS list;    list.head = NULL;    list.push(5);    list.push(20);    list.push(4);    list.push(3);    list.push(30);    cout << "Linked List before sorting" << endl;    list.printlist(list.head);    cout << endl;    list.insertionSort(list.head);    cout << "Linked List After sorting" << endl;    list.printlist(list.head);} // This code is contributed by nirajgusain5
// Java program to sort link list// using insertion sort public class LinkedlistIS{    node head;    node sorted;     class node    {        int val;        node next;         public node(int val)        {            this.val = val;        }    }     void push(int val)    {        /* allocate node */        node newnode = new node(val);        /* link the old list off the new node */        newnode.next = head;        /* move the head to point to the new node */        head = newnode;    }     // function to sort a singly linked list using insertion sort    void insertionSort(node headref)    {        // Initialize sorted linked list        sorted = null;        node current = headref;        // Traverse the given linked list and insert every        // node to sorted        while (current != null)        {            // Store next for next iteration            node next = current.next;            // insert current in sorted linked list            sortedInsert(current);            // Update current            current = next;        }        // Update head_ref to point to sorted linked list        head = 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())     */    void sortedInsert(node newnode)    {        /* Special case for the head end */        if (sorted == null || sorted.val >= newnode.val)        {            newnode.next = sorted;            sorted = newnode;        }        else        {            node current = sorted;            /* Locate the node before the point of insertion */            while (current.next != null && current.next.val < newnode.val)            {                current = current.next;            }            newnode.next = current.next;            current.next = newnode;        }    }     /* Function to print linked list */    void printlist(node head)    {        while (head != null)        {            System.out.print(head.val + " ");            head = head.next;        }    }         // Driver program to test above functions    public static void main(String[] args)    {        LinkedlistIS list = new LinkedlistIS();        list.push(5);        list.push(20);        list.push(4);        list.push(3);        list.push(30);        System.out.println("Linked List before Sorting..");        list.printlist(list.head);        list.insertionSort(list.head);        System.out.println("\nLinkedList After sorting");        list.printlist(list.head);    }} // This code is contributed by Rishabh Mahrsee
# Python implementation of above algorithm # Node classclass 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 # BELOW FUNCTIONS ARE JUST UTILITY TO TEST sortedInsert # Function to print linked list */def 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 listdef push( head_ref, new_data):     # allocate node    new_node = Node(0)     # put in the data    new_node.data = new_data     # link the old list off 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 program to test above functions a = 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("\nLinked List after sorting ")printList(a) # This code is contributed by Arnab Kundu
// C# program to sort link list// using insertion sortusing System; public class LinkedlistIS{    public node head;    public node sorted;     public class node    {        public int val;        public node next;         public node(int val)        {            this.val = val;        }    }     void push(int val)    {        /* allocate node */        node newnode = new node(val);                 /* link the old list off the new node */        newnode.next = head;                 /* move the head to point to the new node */        head = newnode;    }     // function to sort a singly    // linked list using insertion sort    void insertionSort(node headref)    {        // Initialize sorted linked list        sorted = null;        node current = headref;                 // Traverse the given        // linked list and insert every        // node to sorted        while (current != null)        {            // Store next for next iteration            node next = current.next;                         // insert current in sorted linked list            sortedInsert(current);                         // Update current            current = next;        }                 // Update head_ref to point to sorted linked list        head = 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())    */    void sortedInsert(node newnode)    {        /* Special case for the head end */        if (sorted == null || sorted.val >= newnode.val)        {            newnode.next = sorted;            sorted = newnode;        }        else        {            node current = sorted;                         /* Locate the node before the point of insertion */            while (current.next != null &&                    current.next.val < newnode.val)            {                current = current.next;            }            newnode.next = current.next;            current.next = newnode;        }    }     /* Function to print linked list */    void printlist(node head)    {        while (head != null)        {            Console.Write(head.val + " ");            head = head.next;        }    }         // Driver code    public static void Main(String[] args)    {        LinkedlistIS list = new LinkedlistIS();        list.push(5);        list.push(20);        list.push(4);        list.push(3);        list.push(30);        Console.WriteLine("Linked List before Sorting..");        list.printlist(list.head);        list.insertionSort(list.head);        Console.WriteLine("\nLinkedList After sorting");        list.printlist(list.head);    }} // This code contributed by Rajput-Ji
<script>// javascript program to sort link list// using insertion sort var head = null;    var sorted = null;      class node {            constructor(val) {                this.val = val;                this.next = null;            }        }           function push(val) {        /* allocate node */        var newnode = new node(val);        /* link the old list off the new node */        newnode.next = head;        /* move the head to point to the new node */        head = newnode;    }     // function to sort a singly linked list using insertion sort    function insertionSort( headref) {        // Initialize sorted linked list        var sorted = null;        var current = headref;        // Traverse the given linked list and insert every        // node to sorted        while (current != null) {            // Store next for next iteration            var next = current.next;            // insert current in sorted linked list            sortedInsert(current);            // Update current            current = next;        }        // Update head_ref to point to sorted linked list        head = sorted;    }     /*     * function to insert a new_node in a  Note that this function expects a     * pointer to head_ref as this can modify the head of the input linked list     * (similar to push())     */    function sortedInsert( newnode) {        /* Special case for the head end */        if (sorted == null || sorted.val >= newnode.val) {            newnode.next = sorted;            sorted = newnode;        } else {            var current = sorted;            /* Locate the node before the point of insertion */            while (current.next != null && current.next.val < newnode.val) {                current = current.next;            }            newnode.next = current.next;            current.next = newnode;        }    }     /* Function to print linked list */    function printlist( head) {        while (head != null) {            document.write(head.val + " ");            head = head.next;        }    }     // Driver program to test above functions                  push(5);        push(20);        push(4);        push(3);        push(30);        document.write("Linked List before Sorting..<br/>");        printlist(head);        insertionSort(head);        document.write("<br/>LinkedList After sorting<br/>");        printlist(sorted); // This code contributed by aashish1995</script>
Output:  
Linked List before sorting
30  3  4  20  5
Linked List after sorting
3  4  5  20  30
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.
Thus Time Complexity: O(n)*O(n)=O(n^2)
Space Complexity: No extra space is required depending on the size of the input. Thus Space complexity is constant- O(1).
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nidhi_biet
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