Sorted insert for circular linked list

Difficulty Level: Rookie 
Write a C function to insert a new value in a sorted Circular Linked List (CLL). For example, if the input CLL is following.

Algorithm:

Allocate memory for the newly inserted node and put data in the newly allocated node. Let the pointer to the new node be new_node. After memory allocation, following are the three cases that need to be handled.  

1) Linked List is empty:  
    a)  since new_node is the only node in CLL, make a self loop.      
          new_node->next = new_node;  
    b) change the head pointer to point to new node.
          *head_ref = new_node;
2) New node is to be inserted just before the head node:    
  (a) Find out the last node using a loop.
         while(current->next != *head_ref)
            current = current->next;
  (b) Change the next of last node. 
         current->next = new_node;
  (c) Change next of new node to point to head.
         new_node->next = *head_ref;
  (d) change the head pointer to point to new node.
         *head_ref = new_node;
3) New node is to be  inserted somewhere after the head: 
   (a) Locate the node after which new node is to be inserted.
         while ( current->next!= *head_ref && 
             current->next->data < new_node->data)
         {   current = current->next;   }
   (b) Make next of new_node as next of the located pointer
         new_node->next = current->next;
   (c) Change the next of the located pointer
         current->next = new_node;

C++

// C++ program for sorted insert
// in circular linked list
#include <bits/stdc++.h>
using namespace std;

/* structure for a node */
class Node
{
    public:
    int data;
    Node *next;
};

/* function to insert a new_node in a list in sorted way.
Note that this function expects a pointer to head node
as this can modify the head of the input linked list */
void sortedInsert(Node** head_ref, Node* new_node)
{
    Node* current = *head_ref;

    // Case 1 of the above algo
    if (current == NULL)
    {
        new_node->next = new_node;
        *head_ref = new_node;
    }

    // Case 2 of the above algo
    else if (current->data >= new_node->data)
    {
        /* If value is smaller than head's value then
        we need to change next of last node */
        while(current->next != *head_ref)
            current = current->next;
        current->next = new_node;
        new_node->next = *head_ref;
        *head_ref = new_node;
    }

    // Case 3 of the above algo
    else
    {
        /* Locate the node before the point of insertion */
        while (current->next!= *head_ref &&
            current->next->data < new_node->data)
        current = current->next;

        new_node->next = current->next;
        current->next = new_node;
    }
}

/* Function to print nodes in a given linked list */
void printList(Node *start)
{
    Node *temp;

    if(start != NULL)
    {
        temp = start;
        do {
        cout<<temp->data<<" ";
        temp = temp->next;
        } while(temp != start);
    }
}

/* Driver code */
int main()
{
    int arr[] = {12, 56, 2, 11, 1, 90};
    int list_size, i;

    /* start with empty linked list */
    Node *start = NULL;
    Node *temp;

    /* Create linked list from the array arr[].
        Created linked list will be 1->2->11->12->56->90 */
    for (i = 0; i< 6; i++)
    {
        temp = new Node();
        temp->data = arr[i];
        sortedInsert(&start, temp);
    }

    printList(start);

    return 0;
}

// This code is contributed by rathbhupendra.

C

#include<stdio.h>
#include<stdlib.h>

/* structure for a node */
struct Node
{
  int data;
  struct Node *next;
};

/* function to insert a new_node in a list in sorted way.
   Note that this function expects a pointer to head node
   as this can modify the head of the input linked list */
void sortedInsert(struct Node** head_ref, struct Node* new_node)
{
  struct Node* current = *head_ref;

  // Case 1 of the above algo
  if (current == NULL)
  {
     new_node->next = new_node;
     *head_ref = new_node;
  }

  // Case 2 of the above algo
  else if (current->data >= new_node->data)
  {
    /* If value is smaller than head's value then
      we need to change next of last node */
    while(current->next != *head_ref)
        current = current->next;
    current->next = new_node;
    new_node->next = *head_ref;
    *head_ref = new_node;
  }

  // Case 3 of the above algo
  else
  {
    /* Locate the node before the point of insertion */
    while (current->next!= *head_ref &&
           current->next->data < new_node->data)
      current = current->next;

    new_node->next = current->next;
    current->next = new_node;
  }
}

/* Function to print nodes in a given linked list */
void printList(struct Node *start)
{
  struct Node *temp;

  if(start != NULL)
  {
    temp = start;
    printf("\n");
    do {
      printf("%d ", temp->data);
      temp = temp->next;
    } while(temp != start);
  }
}

/* Driver program to test above functions */
int main()
{
  int arr[] = {12, 56, 2, 11, 1, 90};
  int list_size, i;

  /* start with empty linked list */
  struct Node *start = NULL;
  struct Node *temp;

  /* Create linked list from the array arr[].
    Created linked list will be 1->2->11->12->56->90 */
  for (i = 0; i< 6; i++)
  {
    temp = (struct Node *)malloc(sizeof(struct Node));
    temp->data = arr[i];
    sortedInsert(&start, temp);
  }

  printList(start);

  return 0;
}

Java

// Java program for sorted insert in circular linked list

class Node
{
    int data;
    Node next;

    Node(int d)
    {
        data = d;
        next = null;
    }
}

class LinkedList
{
    Node head;

    // Constructor
    LinkedList()   { head = null; }

    /* function to insert a new_node in a list in sorted way.
     Note that this function expects a pointer to head node
     as this can modify the head of the input linked list */
    void sortedInsert(Node new_node)
    {
        Node current = head;

        // Case 1 of the above algo
        if (current == null)
        {
            new_node.next = new_node;
            head = new_node;

        }

        // Case 2 of the above algo
        else if (current.data >= new_node.data)
        {

            /* If value is smaller than head's value then
             we need to change next of last node */
            while (current.next != head)
                current = current.next;

            current.next = new_node;
            new_node.next = head;
            head = new_node;
        }

        // Case 3 of the above algo
        else
        {

            /* Locate the node before the point of insertion */
            while (current.next != head &&
                   current.next.data < new_node.data)
                current = current.next;

            new_node.next = current.next;
            current.next = new_node;
        }
    }

    // Utility method to print a linked list
    void printList()
    {
        if (head != null)
        {
            Node temp = head;
            do
            {
                System.out.print(temp.data + " ");
                temp = temp.next;
            }  while (temp != head);
        }
    }

    // Driver code to test above
    public static void main(String[] args)
    {
        LinkedList list = new LinkedList();

        // Creating the linkedlist
        int arr[] = new int[] {12, 56, 2, 11, 1, 90};

        /* start with empty linked list */
        Node temp = null;

        /* Create linked list from the array arr[].
         Created linked list will be 1->2->11->12->56->90*/
        for (int i = 0; i < 6; i++)
        {
            temp = new Node(arr[i]);
            list.sortedInsert(temp);
        }

        list.printList();
    }
}

// This code has been contributed by Mayank Jaiswal

Python3

# Node class
class Node:

    # Constructor to initialize the node object
    def __init__(self, data):
        self.data = data
        self.next = None

class LinkedList:

    # Function to initialize head
    def __init__(self):
        self.head = None

    # Function to insert a new node at the beginning
    def push(self, new_data):
        new_node = Node(new_data)
        new_node.next = self.head
        self.head = new_node

    # Utility function to print the linked LinkedList
    def printList(self):
        temp = self.head
        print(temp.data,end=' ')
        temp = temp.next
        while(temp != self.head):
            print (temp.data,end=' ')
            temp = temp.next

    """ function to insert a new_node in a list in sorted way.
       Note that this function expects a pointer to head node
       as this can modify the head of the input linked list """
    def sortedInsert(self, new_node):

        current = self.head

        # Case 1 of the above algo
        if current is None:
            new_node.next = new_node
            self.head = new_node

        # Case 2 of the above algo
        elif (current.data >= new_node.data):

            # If value is smaller than head's value then we
            # need to change next of last node
            while current.next != self.head :
                current = current.next
            current.next = new_node
            new_node.next = self.head
            self.head = new_node


        # Case 3 of the above algo
        else:

            # Locate the node before the point of insertion
            while (current.next != self.head  and
                   current.next.data < new_node.data):
                current = current.next

            new_node.next = current.next
            current.next = new_node


# Driver program to test the above function
#llist = LinkedList()
arr = [12, 56, 2, 11, 1, 90]

list_size = len(arr)

# start with empty linked list
start = LinkedList()

# Create linked list from the array arr[]
# Created linked list will be 1->2->11->12->56->90
for i in range(list_size):
    temp = Node(arr[i])
    start.sortedInsert(temp)

start.printList()

# This code is contributed by Nikhil Kumar Singh(nickzuck_007)

C#

// C# program for sorted insert
// in circular linked list
using System;

class LinkedList
{
    public class Node
    {
        public int data;
        public Node next;

        public Node(int d)
        {
            data = d;
            next = null;
        }
    }
    Node head;

    // Constructor
    LinkedList()
    {
        head = null;
    }

    /* function to insert a new_node
      in a list in sorted way. Note that
      this function expects a pointer
      to head node as this can modify
      the head of the input linked list */
    void sortedInsert(Node new_node)
    {
        Node current = head;

        // Case 1 of the above algo
        if (current == null)
        {
            new_node.next = new_node;
            head = new_node;

        }

        // Case 2 of the above algo
        else if (current.data >= new_node.data)
        {

            /* If value is smaller than
                head's value then we need
                to change next of last node */
            while (current.next != head)
                current = current.next;

            current.next = new_node;
            new_node.next = head;
            head = new_node;
        }

        // Case 3 of the above algo
        else
        {

            /* Locate the node before
            the point of insertion */
            while (current.next != head &&
                current.next.data < new_node.data)
                current = current.next;

            new_node.next = current.next;
            current.next = new_node;
        }
    }

    // Utility method to print a linked list
    void printList()
    {
        if (head != null)
        {
            Node temp = head;
            do
            {
                Console.Write(temp.data + " ");
                temp = temp.next;
            }
            while (temp != head);
        }
    }

    // Driver code
    public static void Main(String []args)
    {
        LinkedList list = new LinkedList();

        // Creating the linkedlist
        int []arr = {12, 56, 2, 11, 1, 90};

        /* start with empty linked list */
        Node temp = null;

        /* Create linked list from the
          array arr[]. Created linked list
          will be 1->2->11->12->56->90*/
        for (int i = 0; i < 6; i++)
        {
            temp = new Node(arr[i]);
            list.sortedInsert(temp);
        }
        list.printList();
    }
}

// This code has been contributed
// by Arnab Kundu

Javascript

<script>
// javascript program for sorted insert in circular linked list

class Node {
    constructor(val) {
        this.data = val;
        this.next = null;
    }
}

var head = null;


    /*
     * function to insert a new_node in a list in sorted way.
     * Note that this function expects a pointer to head node
     * as this can modify the head of the
     * input linked list
     */
    function sortedInsert(new_node) {
    var current = head;

        // Case 1 of the above algo
        if (current == null) {
            new_node.next = new_node;
            head = new_node;

        }

        // Case 2 of the above algo
        else if (current.data >= new_node.data) {

            /*
             * If value is smaller than head's value then we
             * need to change next of last node
             */
            while (current.next != head)
                current = current.next;

            current.next = new_node;
            new_node.next = head;
            head = new_node;
        }

        // Case 3 of the above algo
        else {

            /* Locate the node before the point of insertion */
            while (current.next != head && current.next.data < new_node.data)
                current = current.next;

            new_node.next = current.next;
            current.next = new_node;
        }
    }

    // Utility method to print a linked list
    function printList() {
        if (head != null) {
    var temp = head;
            do {
                document.write(temp.data + " ");
                temp = temp.next;
            } while (temp != head);
        }
    }

    // Driver code to test above


        // Creating the linkedlist
        var arr = [ 12, 56, 2, 11, 1, 90 ];

        /* start with empty linked list */
        var temp = null;

        /*
         * Create linked list from the array arr.
         * Created linked list will be
         * 1->2->11->12->56->90
         */
        for (i = 0; i < 6; i++) {
            temp = new Node(arr[i]);
            sortedInsert(temp);
        }

        printList();

// This code contributed by umadevi9616
</script>

Output:

1 2 11 12 56 90

Time Complexity: O(n)

Here n is the number of nodes in the given linked list.

Auxiliary Space: O(1).

As constant extra space is used.

Case 2 of the above algorithm/code can be optimized. To implement the suggested change we need to modify case 2 to follow. 

C

// Case 2 of the above algo
else if (current->data >= new_node->data)
{
  // swap the data part of head node and new node
  // assuming that we have a function swap(int *, int *)
  swap(&(current->data), &(new_node->data));

  new_node->next = (*head_ref)->next;
  (*head_ref)->next = new_node;
}

C++

  // Case 2 of the above algo
  else if (current->data >= new_node->data)
  {
    // swap the data part of head node and new node
    // assuming that we have a function swap(int *, int *)
    swap(&(current->data), &(new_node->data));

    new_node->next = (*head_ref)->next;
    (*head_ref)->next = new_node;
  }
// this code is contributed by devendra salunke

Java

// Case 2 of the above algo
else if (current.data >= new_node.data)
{
  // swap the data part of head node and new node
  // assuming that we have a function swap(int *, int *)
  Node tmp = current.data;
  current.data = new_node.data;
  new_node.data = tmp;
  new_node.next = (head_ref).next;
  (head_ref).next = new_node;
}

// This code is contributed by pratham76.

Python3

# Case 2 of the above algo
elif (current.data >= new_node.data):

  # swap the data part of head node and new node
  # assuming that we have a function swap(int *, int *)
  tmp = current.data;
  current.data = new_node.data;
  new_node.data = tmp;
  new_node.next = (head_ref).next;
  (head_ref).next = new_node;

# This code is contributed by _saurabh_jaiswal

C#

// Case 2 of the above algo
else if (current.data >= new_node.data)
{
  // swap the data part of head node and new node
  // assuming that we have a function swap(int *, int *)
  Node tmp = current.data;
  current.data = new_node.data;
  new_node.data = tmp;
  new_node.next = (head_ref).next;
  (head_ref).next = new_node;
}

// This code is contributed by rutvik_56

Javascript

<script>

// Case 2 of the above algo
else if (current.data >= new_node.data)
{
  // swap the data part of head node and new node
  // assuming that we have a function swap(int *, int *)
  let tmp = current.data;
  current.data = new_node.data;
  new_node.data = tmp;
  new_node.next = (head_ref).next;
  (head_ref).next = new_node;
}

// This code is contributed by avanitrachhadiya2155

</script>

In the previous approach the time complexity of case 2 was O(n) which is reduced to O(1) using this approach.

The auxiliary space used here is O(1) which is same as previous approach.

Please write comments if you find the above code/algorithm incorrect, or find other ways to solve the same problem.