Count rotations in sorted and rotated linked list

Given a linked list of n nodes which is first sorted, then rotated by k elements. Find the value of k.

The idea is to traverse singly linked list to check condition whether current node value is greater than value of next node. If the given condition is true, then break the loop. Otherwise increase the counter variable and increase the node by node->next. Below is the implementation of this approach.

Implementation:

C++

// Program for count number of rotations in
// sorted linked list.
#include <bits/stdc++.h>
using namespace std;
/* Linked list node */
struct Node {
    int data;
    struct Node* next;
};

// Function that count number of
// rotation in singly linked list.
int countRotation(struct Node* head)
{
    // declare count variable and assign it 1.
    int count = 0;

    // declare a min variable and assign to
    // data of head node.
    int min = head->data;

    // check that while head not equal to NULL.
    while (head != NULL) {

        // if min value is greater then head->data
        // then it breaks the while loop and
        // return the value of count.
        if (min > head->data)
            break;

        count++;

        // head assign the next value of head.
        head = head->next;
    }
    return count;
}

// Function to push element in linked list.
void push(struct Node** head, int data)
{
    // Allocate dynamic memory for newNode.
    struct Node* newNode = new Node;

    // Assign the data into newNode.
    newNode->data = data;

    // newNode->next assign the address of
    // head node.
    newNode->next = (*head);

    // newNode become the headNode.
    (*head) = newNode;
}

// Display linked list.
void printList(struct Node* node)
{
    while (node != NULL) {
        printf("%d ", node->data);
        node = node->next;
    }
}

// Driver functions
int main()
{
    // Create a node and initialize with NULL
    struct Node* head = NULL;

    // push() insert node in linked list.
    // 15 -> 18 -> 5 -> 8 -> 11 -> 12
    push(&head, 12);
    push(&head, 11);
    push(&head, 8);
    push(&head, 5);
    push(&head, 18);
    push(&head, 15);

    printList(head);
    cout << endl;
    cout << "Linked list rotated elements: ";

    // Function call countRotation()
    cout << countRotation(head) << endl;

    return 0;
}

Java

// Program for count number of rotations in
// sorted linked list.
import java.util.*;

class GFG
{

/* Linked list node */
static class Node {
    int data;
    Node next;
};

// Function that count number of
// rotation in singly linked list.
static int countRotation(Node head)
{

    // declare count variable and assign it 1.
    int count = 0;

    // declare a min variable and assign to
    // data of head node.
    int min = head.data;

    // check that while head not equal to null.
    while (head != null) {

        // if min value is greater then head.data
        // then it breaks the while loop and
        // return the value of count.
        if (min > head.data)
            break;

        count++;

        // head assign the next value of head.
        head = head.next;
    }
    return count;
}

// Function to push element in linked list.
static Node push(Node head, int data)
{
    // Allocate dynamic memory for newNode.
    Node newNode = new Node();

    // Assign the data into newNode.
    newNode.data = data;

    // newNode.next assign the address of
    // head node.
    newNode.next = (head);

    // newNode become the headNode.
    (head) = newNode;
    return head;
}

// Display linked list.
static void printList(Node node)
{
    while (node != null) {
        System.out.printf("%d ", node.data);
        node = node.next;
    }
}

// Driver functions
public static void main(String[] args)
{

    // Create a node and initialize with null
    Node head = null;

    // push() insert node in linked list.
    // 15.18.5.8.11.12
    head = push(head, 12);
    head = push(head, 11);
    head = push(head, 8);
    head = push(head, 5);
    head = push(head, 18);
    head = push(head, 15);

    printList(head);
    System.out.println();
    System.out.print("Linked list rotated elements: ");

    // Function call countRotation()
    System.out.print(countRotation(head) +"\n");

}
}

// This code contributed by gauravrajput1

Python3

# Program for count number of rotations in
# sorted linked list.

# Linked list node
class Node:

    def __init__(self, data):

        self.data = data
        self.next = None

# Function that count number of
# rotation in singly linked list.
def countRotation(head):

    # Declare count variable and assign it 1.
    count = 0

    # Declare a min variable and assign to
    # data of head node.
    min = head.data

    # Check that while head not equal to None.
    while (head != None):

        # If min value is greater then head->data
        # then it breaks the while loop and
        # return the value of count.
        if (min > head.data):
            break

        count += 1

        # head assign the next value of head.
        head = head.next

    return count

# Function to push element in linked list.
def push(head, data):

    # Allocate dynamic memory for newNode.
    newNode = Node(data)

    # Assign the data into newNode.
    newNode.data = data

    # newNode->next assign the address of
    # head node.
    newNode.next = (head)

    # newNode become the headNode.
    (head) = newNode
    return head

# Display linked list.
def printList(node):

    while (node != None):
        print(node.data, end = ' ')
        node = node.next

# Driver code
if __name__=='__main__':

    # Create a node and initialize with None
    head = None

    # push() insert node in linked list.
    # 15 -> 18 -> 5 -> 8 -> 11 -> 12
    head = push(head, 12)
    head = push(head, 11)
    head = push(head, 8)
    head = push(head, 5)
    head = push(head, 18)
    head = push(head, 15)

    printList(head);
    print()
    print("Linked list rotated elements: ",
          end = '')

    # Function call countRotation()
    print(countRotation(head))

# This code is contributed by rutvik_56

C#

// Program for count number of rotations in
// sorted linked list.
using System;
class LinkedList{

// Head of linked list
Node head;

// Linked list node
class Node
{
    public int data;
    public Node next;

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

int countRotation()
{
    // declare count variable and assign it 1.
    int count = 0;

    // declare a min variable and assign to
    // data of head node.
    int min = head.data;

    // check that while head not equal to NULL.
    while (head != null) {

        // if min value is greater then head->data
        // then it breaks the while loop and
        // return the value of count.
        if (min > head.data)
            break;

        count++;

        // head assign the next value of head.
        head = head.next;
    }
    return count;
}

// Inserts a new Node at front of the list.
public void push(int new_data)
{

    /* 1 & 2: Allocate the Node &
              Put in the data*/
    Node new_node = new Node(new_data);

    /* 3. Make next of new Node as head */
    new_node.next = head;

    /* 4. Move the head to point to new Node */
    head = new_node;
}

// Function that count number of
// rotation in singly linked list.
public void printList()
{
    Node tnode = head;
    while (tnode != null)
    {
        Console.Write(tnode.data + "->");
        tnode = tnode.next;
    }
    Console.WriteLine("NULL");
}

// Driver code
static public void Main()
{
    LinkedList llist = new LinkedList();

    llist.push(12);
    llist.push(11);
    llist.push(8);
    llist.push(5);
    llist.push(18);
    llist.push(15);

    llist.printList();
    Console.Write("Linked list rotated elements: ");
    Console.WriteLine(llist.countRotation());
}
}

// This code is contributed by Aarti_Rathi

Javascript

<script>

// Program for count number of rotations in
// sorted linked list.

/* Linked list node */
class Node
{
    constructor()
    {
        this.data=0;
        this.next=null;
    }
}

// Function that count number of
// rotation in singly linked list.
function countRotation(head)
{
    // declare count variable and assign it 1.
    let count = 0;

    // declare a min variable and assign to
    // data of head node.
    let min = head.data;

    // check that while head not equal to null.
    while (head != null) {

        // if min value is greater then head.data
        // then it breaks the while loop and
        // return the value of count.
        if (min > head.data)
            break;

        count++;

        // head assign the next value of head.
        head = head.next;
    }
    return count;
}

// Function to push element in linked list.
function push(head,data)
{
    // Allocate dynamic memory for newNode.
    let newNode = new Node();

    // Assign the data into newNode.
    newNode.data = data;

    // newNode.next assign the address of
    // head node.
    newNode.next = (head);

    // newNode become the headNode.
    (head) = newNode;
    return head;
}

// Display linked list.
function printList(node)
{
    while (node != null) {
        document.write(node.data+" ");
        node = node.next;
    }
}

// Driver functions
// Create a node and initialize with null
let head = null;

// push() insert node in linked list.
// 15.18.5.8.11.12
head = push(head, 12);
head = push(head, 11);
head = push(head, 8);
head = push(head, 5);
head = push(head, 18);
head = push(head, 15);

printList(head);
document.write("<br>");
document.write("Linked list rotated elements: ");

// Function call countRotation()
document.write(countRotation(head) +"<br>");


// This code is contributed by unknown2108

</script>

Output

15 18 5 8 11 12 
Linked list rotated elements: 2

Time Complexity: O(N), where N represents the length of the linked list.
Auxiliary Space: O(1), no extra space is required, so it is a constant.

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