Sorted insert for circular linked list

2.2

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.

After insertion of 7, the above CLL should be changed to 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

#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

Python

# 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,
        temp = temp.next
        while(temp != self.head):
            print temp.data,
            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)


Output:

1 2 11 12 56 90

Time Complexity: O(n) where n is the number of nodes in the given linked list.

Case 2 of the above algorithm/code can be optimized. Please see this comment from Pavan. To implement the suggested change we need to modify the case 2 to following.

  
  // 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;
  }

Asked in: Amazon, Microsoft

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

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