Sort Linked List containing values from 1 to N

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Given a linked list of size N containing all values from 1 to N. The task is to sort the linked list in increasing order.

Examples:

Input : List = 3 -> 5 -> 4 -> 6 -> 1 -> 2
Output : 1 -> 2 -> 3 -> 4 -> 5 -> 6

Input : List = 5 -> 4 -> 3 -> 2 -> 1
Output : 1 -> 2 -> 3 -> 4 -> 5

Naive approach: The simplest approach is to sort this linked list with the use of any type of sorting method. It takes O(N*logN) minimum time.

Efficient approach: An efficient approach is to observe that the linked list contains a total of N elements and elements are numbered from 1 to N. Traverse the linked list and replace every element with its position.

Below is the implementation of this approach:

C++

// C++ program to sort linked list containing
// values from 1 to N
#include <iostream>
 
using namespace std;
 
// A linked list node
struct Node {
    int data;
    struct Node* next;
};
 
// Function to sort linked list
bool sortList(struct Node* head)
{
    int startVal = 1;
 
    while (head != NULL) {
        head->data = startVal;
 
        startVal++;
 
        head = head->next;
    }
}
 
// Function to add a node at the
// beginning of Linked List
void push(struct Node** head_ref, int new_data)
{
    /* allocate node */
    struct Node* new_node = (struct Node*)malloc(sizeof(struct Node));
 
    /* 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;
}
 
// This function prints contents of
// linked list starting from
// the given node
void printList(struct Node* node)
{
    while (node != NULL) {
        cout << node->data << " ";
 
        node = node->next;
    }
}
 
// Driver program to test above function
int main()
{
    struct Node* start = NULL;
 
    /* The constructed linked list is: 
    3->5->4->6->1->2 */
    push(&start, 2);
    push(&start, 1);
    push(&start, 6);
    push(&start, 4);
    push(&start, 5);
    push(&start, 3);
 
    sortList(start);
 
    printList(start);
 
    return 0;
}

Java

// Java program to sort linked list containing
// values from 1 to N
import java.util.*;
class GFG 
{
 
/* Link list node */
static class Node
{
    int data;
    Node next;
};
static Node start;
 
// Function to sort linked list
static void sortList(Node head)
{
    int startVal = 1;
 
    while (head != null)
    {
        head.data = startVal;
 
        startVal++;
 
        head = head.next;
    }
}
 
// Function to add a node at the
// beginning of Linked List
static void push(Node head_ref, 
                 int new_data)
{
    /* allocate node */
    Node new_node = new Node();
 
    /* 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;
    start = head_ref;
}
 
// This function prints contents of
// linked list starting from
// the given node
static void printList(Node node)
{
    while (node != null)
    {
        System.out.print(node.data + " ");
 
        node = node.next;
    }
}
 
// Driver Code
public static void main(String[] args) 
{
    start = null;
 
    /* The constructed linked list is: 
    3->5->4->6->1->2 */
    push(start, 2);
    push(start, 1);
    push(start, 6);
    push(start, 4);
    push(start, 5);
    push(start, 3);
 
    sortList(start);
 
    printList(start);
}
}
 
// This code is contributed by PrinciRaj1992 

Python3

# Python3 program to sort linked list 
# containing values from 1 to N
import math
 
# A linked list node
class Node: 
    def __init__(self, data): 
        self.data = data 
        self.next = None
 
# Function to sort linked list
def sortList(head):
    startVal = 1
 
    while (head != None):
        head.data = startVal
 
        startVal = startVal + 1
 
        head = head.next
     
# Function to add a node at the
# beginning of Linked List
def push(head_ref, new_data):
     
    # allocate node 
    new_node = Node(new_data)
 
    # 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
 
# This function prints contents of
# linked list starting from
# the given node
def printList(node):
    while (node != None):
        print(node.data, end = " ")
 
        node = node.next
     
# Driver Code
if __name__=='__main__':
    head = None
 
    # The constructed linked list is: 
    #3.5.4.6.1.2 
    head = push(head, 2)
    head = push(head, 1)
    head = push(head, 6)
    head = push(head, 4)
    head = push(head, 5)
    head = push(head, 3)
 
    sortList(head)
 
    printList(head)
 
# This code is contributed by Srathore

C#

// C# program to sort linked list 
// containing values from 1 to N
using System;
     
class GFG 
{
 
/* Link list node */
public class Node
{
    public int data;
    public Node next;
};
static Node start;
 
// Function to sort linked list
static void sortList(Node head)
{
    int startVal = 1;
 
    while (head != null)
    {
        head.data = startVal;
 
        startVal++;
 
        head = head.next;
    }
}
 
// Function to add a node at the
// beginning of Linked List
static void push(Node head_ref, 
                 int new_data)
{
    /* allocate node */
    Node new_node = new Node();
 
    /* 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;
    start = head_ref;
}
 
// This function prints contents of
// linked list starting from
// the given node
static void printList(Node node)
{
    while (node != null)
    {
        Console.Write(node.data + " ");
 
        node = node.next;
    }
}
 
// Driver Code
public static void Main(String[] args) 
{
    start = null;
 
    /* The constructed linked list is: 
    3->5->4->6->1->2 */
    push(start, 2);
    push(start, 1);
    push(start, 6);
    push(start, 4);
    push(start, 5);
    push(start, 3);
 
    sortList(start);
 
    printList(start);
}
}
 
// This code is contributed 
// by Princi Singh

Javascript

<script>
 
      // JavaScript program to sort linked list
      // containing values from 1 to N
      /* Link list node */
      class Node {
        constructor() {
          this.data = 0;
          this.next = null;
        }
      }
      var start = null;
 
      // Function to sort linked list
      function sortList(head) {
        var startVal = 1;
 
        while (head != null) {
          head.data = startVal;
 
          startVal++;
 
          head = head.next;
        }
      }
 
      // Function to add a node at the
      // beginning of Linked List
      function push(head_ref, new_data) {
        /* allocate node */
        var new_node = new Node();
 
        /* 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;
        start = head_ref;
      }
 
      // This function prints contents of
      // linked list starting from
      // the given node
      function printList(node) {
        while (node != null) {
          document.write(node.data + " ");
 
          node = node.next;
        }
      }
 
      // Driver Code
      start = null;
 
      /* The constructed linked list is:
    3->5->4->6->1->2 */
      push(start, 2);
      push(start, 1);
      push(start, 6);
      push(start, 4);
      push(start, 5);
      push(start, 3);
 
      sortList(start);
 
      printList(start);
       
</script>

Output

1 2 3 4 5 6

Complexity Analysis:

Time Complexity: O(n)
Auxiliary Space: O(1)

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