Sort Linked List containing values from 1 to N

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++

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// 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 off 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;
}

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Java

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// 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 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)
    {
        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 

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C#

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// 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

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Output:

1 2 3 4 5 6


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