Recursive selection sort for singly linked list | Swapping node links

Last Updated : 14 Jul, 2022

Given a singly linked list containing n nodes. The problem is to sort the list using the recursive selection sort technique. The approach should be such that it involves swapping node links instead of swapping node data.

sorting image

Examples:

Input : 10 -> 12 -> 8 -> 4 -> 6 Output : 4 -> 6 -> 8 -> 10 -> 12

In Selection Sort, we first find the minimum element, swap it with the beginning node and recur for the remaining list. Below is the recursive implementation of these steps for the linked list.

recurSelectionSort(head)      if head->next == NULL          return head      Initialize min = head      Initialize beforeMin = NULL      Initialize ptr = head           while ptr->next != NULL           if min->data > ptr->next->data          min = ptr->next          beforeMin = ptr      ptr = ptr->next               if min != head          swapNodes(&head, head, min, beforeMin)           head->next = recurSelectionSort(head->next)      return head  swapNodes(head_ref, currX, currY, prevY)      head_ref = currY      prevY->next = currX       Initialize temp = currY->next      currY->next = currX->next      currX->next  = temp

The swapNodes(head_ref, currX, currY, prevY) is based on the approach discussed here but it has been modified accordingly for the implementation of this post.

Implementation:

C++

   // C++ implementation of recursive selection sort
// for singly linked list | Swapping node links
#include <bits/stdc++.h>
using namespace std;
 
// A Linked list node
struct Node {
    int data;
    struct Node* next;
};
 
// function to swap nodes 'currX' and 'currY' in a
// linked list without swapping data
void swapNodes(struct Node** head_ref, struct Node* currX,
               struct Node* currY, struct Node* prevY)
{
    // make 'currY' as new head
    *head_ref = currY;
 
    // adjust links
    prevY->next = currX;
 
    // Swap next pointers
    struct Node* temp = currY->next;
    currY->next = currX->next;
    currX->next = temp;
}
 
// function to sort the linked list using
// recursive selection sort technique
struct Node* recurSelectionSort(struct Node* head)
{
    // if there is only a single node
    if (head->next == NULL)
        return head;
 
    // 'min' - pointer to store the node having
    // minimum data value
    struct Node* min = head;
 
    // 'beforeMin' - pointer to store node previous
    // to 'min' node
    struct Node* beforeMin = NULL;
    struct Node* ptr;
 
    // traverse the list till the last node
    for (ptr = head; ptr->next != NULL; ptr = ptr->next) {
 
        // if true, then update 'min' and 'beforeMin'
        if (ptr->next->data < min->data) {
            min = ptr->next;
            beforeMin = ptr;
        }
    }
 
    // if 'min' and 'head' are not same,
    // swap the head node with the 'min' node
    if (min != head)
        swapNodes(&head, head, min, beforeMin);
 
    // recursively sort the remaining list
    head->next = recurSelectionSort(head->next);
 
    return head;
}
 
// function to sort the given linked list
void sort(struct Node** head_ref)
{
    // if list is empty
    if ((*head_ref) == NULL)
        return;
 
    // sort the list using recursive selection
    // sort technique
    *head_ref = recurSelectionSort(*head_ref);
}
 
// function to insert a node at the
// beginning of the 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 to the new node
    new_node->next = (*head_ref);
 
    // move the head to point to the new node
    (*head_ref) = new_node;
}
 
// function to print the linked list
void printList(struct Node* head)
{
    while (head != NULL) {
        cout << head->data << " ";
        head = head->next;
    }
}
 
// Driver program to test above
int main()
{
    struct Node* head = NULL;
 
    // create linked list 10->12->8->4->6
    push(&head, 6);
    push(&head, 4);
    push(&head, 8);
    push(&head, 12);
    push(&head, 10);
 
    cout << "Linked list before sorting:n";
    printList(head);
 
    // sort the linked list
    sort(&head);
 
    cout << "\nLinked list after sorting:n";
    printList(head);
 
    return 0;
}
 
  

Java

   // Java implementation of recursive selection sort 
// for singly linked list | Swapping node links 
class GFG
{
     
// A Linked list node 
static class Node
{ 
    int data; 
    Node next; 
}; 
 
// function to swap nodes 'currX' and 'currY' in a 
// linked list without swapping data 
static Node swapNodes( Node head_ref, Node currX, 
                        Node currY, Node prevY) 
{ 
    // make 'currY' as new head 
    head_ref = currY; 
 
    // adjust links 
    prevY.next = currX; 
 
    // Swap next pointers 
    Node temp = currY.next; 
    currY.next = currX.next; 
    currX.next = temp; 
    return head_ref;
} 
 
// function to sort the linked list using 
// recursive selection sort technique 
static Node recurSelectionSort( Node head) 
{ 
    // if there is only a single node 
    if (head.next == null) 
        return head; 
 
    // 'min' - pointer to store the node having 
    // minimum data value 
    Node min = head; 
 
    // 'beforeMin' - pointer to store node previous 
    // to 'min' node 
    Node beforeMin = null; 
    Node ptr; 
 
    // traverse the list till the last node 
    for (ptr = head; ptr.next != null; ptr = ptr.next) 
    { 
 
        // if true, then update 'min' and 'beforeMin' 
        if (ptr.next.data < min.data) 
        { 
            min = ptr.next; 
            beforeMin = ptr; 
        } 
    } 
 
    // if 'min' and 'head' are not same, 
    // swap the head node with the 'min' node 
    if (min != head) 
        head = swapNodes(head, head, min, beforeMin); 
 
    // recursively sort the remaining list 
    head.next = recurSelectionSort(head.next); 
 
    return head; 
} 
 
// function to sort the given linked list 
static Node sort( Node head_ref) 
{ 
    // if list is empty 
    if ((head_ref) == null) 
        return null; 
 
    // sort the list using recursive selection 
    // sort technique 
    head_ref = recurSelectionSort(head_ref); 
    return head_ref;
} 
 
// function to insert a node at the 
// beginning of the linked list 
static Node 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 to the new node 
    new_node.next = (head_ref); 
 
    // move the head to point to the new node 
    (head_ref) = new_node; 
    return head_ref;
} 
 
// function to print the linked list 
static void printList( Node head) 
{ 
    while (head != null) 
    { 
        System.out.print( head.data + " "); 
        head = head.next; 
    } 
} 
 
// Driver code 
public static void main(String args[])
{ 
    Node head = null; 
 
    // create linked list 10.12.8.4.6 
    head = push(head, 6); 
    head = push(head, 4); 
    head = push(head, 8); 
    head = push(head, 12); 
    head = push(head, 10); 
 
    System.out.println( "Linked list before sorting:"); 
    printList(head); 
 
    // sort the linked list 
    head = sort(head); 
 
    System.out.print( "\nLinked list after sorting:"); 
    printList(head); 
} 
} 
 
// This code is contributed by Arnab Kundu
 
  

Python

   # Python implementation of recursive selection sort 
# for singly linked list | Swapping node links 
 
# Linked List node 
class Node: 
    def __init__(self, data): 
        self.data = data 
        self.next = None
 
# function to swap nodes 'currX' and 'currY' in a 
# linked list without swapping data 
def swapNodes(head_ref, currX, currY, prevY) :
 
    # make 'currY' as new head 
    head_ref = currY 
 
    # adjust links 
    prevY.next = currX 
 
    # Swap next pointers 
    temp = currY.next
    currY.next = currX.next
    currX.next = temp 
    return head_ref
 
# function to sort the linked list using 
# recursive selection sort technique 
def recurSelectionSort( head) :
 
    # if there is only a single node 
    if (head.next == None) :
        return head 
 
    # 'min' - pointer to store the node having 
    # minimum data value 
    min = head 
 
    # 'beforeMin' - pointer to store node previous 
    # to 'min' node 
    beforeMin = None
    ptr = head
     
    # traverse the list till the last node 
    while ( ptr.next != None ) :
     
        # if true, then update 'min' and 'beforeMin' 
        if (ptr.next.data < min.data) :
         
            min = ptr.next
            beforeMin = ptr 
             
        ptr = ptr.next
     
    # if 'min' and 'head' are not same, 
    # swap the head node with the 'min' node 
    if (min != head) :
        head = swapNodes(head, head, min, beforeMin) 
 
    # recursively sort the remaining list 
    head.next = recurSelectionSort(head.next) 
 
    return head 
 
# function to sort the given linked list 
def sort( head_ref) :
 
    # if list is empty 
    if ((head_ref) == None) :
        return None
 
    # sort the list using recursive selection 
    # sort technique 
    head_ref = recurSelectionSort(head_ref) 
    return head_ref
 
# function to insert a node at the 
# beginning of the linked list 
def push( head_ref, new_data) :
 
    # allocate node 
    new_node = Node(0) 
 
    # put in the data 
    new_node.data = new_data 
 
    # link the old list to the new node 
    new_node.next = (head_ref) 
 
    # move the head to point to the new node 
    (head_ref) = new_node 
    return head_ref
 
# function to print the linked list 
def printList( head) :
 
    while (head != None) :
     
        print( head.data ,end = " ") 
        head = head.next
     
# Driver code 
head = None
 
# create linked list 10.12.8.4.6 
head = push(head, 6) 
head = push(head, 4) 
head = push(head, 8) 
head = push(head, 12) 
head = push(head, 10) 
 
print( "Linked list before sorting:") 
printList(head) 
 
# sort the linked list 
head = sort(head) 
 
print( "\nLinked list after sorting:") 
printList(head) 
 
# This code is contributed by Arnab Kundu
 
  

C#

   // C# implementation of recursive selection sort 
// for singly linked list | Swapping node links 
using System;
public class GFG
{
     
// A Linked list node 
public class Node
{ 
    public int data; 
    public Node next; 
}; 
 
// function to swap nodes 'currX' and 'currY' in a 
// linked list without swapping data 
static Node swapNodes(Node head_ref, Node currX, 
                      Node currY, Node prevY) 
{ 
    // make 'currY' as new head 
    head_ref = currY; 
 
    // adjust links 
    prevY.next = currX; 
 
    // Swap next pointers 
    Node temp = currY.next; 
    currY.next = currX.next; 
    currX.next = temp; 
    return head_ref;
} 
 
// function to sort the linked list using 
// recursive selection sort technique 
static Node recurSelectionSort(Node head) 
{ 
    // if there is only a single node 
    if (head.next == null) 
        return head; 
 
    // 'min' - pointer to store the node having 
    // minimum data value 
    Node min = head; 
 
    // 'beforeMin' - pointer to store node 
    // previous to 'min' node 
    Node beforeMin = null; 
    Node ptr; 
 
    // traverse the list till the last node 
    for (ptr = head; ptr.next != null; 
                     ptr = ptr.next) 
    { 
 
        // if true, then update 'min' and 'beforeMin' 
        if (ptr.next.data < min.data) 
        { 
            min = ptr.next; 
            beforeMin = ptr; 
        } 
    } 
 
    // if 'min' and 'head' are not same, 
    // swap the head node with the 'min' node 
    if (min != head) 
        head = swapNodes(head, head, min, beforeMin); 
 
    // recursively sort the remaining list 
    head.next = recurSelectionSort(head.next); 
 
    return head; 
} 
 
// function to sort the given linked list 
static Node sort( Node head_ref) 
{ 
    // if list is empty 
    if ((head_ref) == null) 
        return null; 
 
    // sort the list using recursive selection 
    // sort technique 
    head_ref = recurSelectionSort(head_ref); 
    return head_ref;
} 
 
// function to insert a node at the 
// beginning of the linked list 
static Node 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 to the new node 
    new_node.next = (head_ref); 
 
    // move the head to point to the new node 
    (head_ref) = new_node; 
    return head_ref;
} 
 
// function to print the linked list 
static void printList( Node head) 
{ 
    while (head != null) 
    { 
        Console.Write(head.data + " "); 
        head = head.next; 
    } 
} 
 
// Driver code 
public static void Main(String []args)
{ 
    Node head = null; 
 
    // create linked list 10->12->8->4->6
    head = push(head, 6); 
    head = push(head, 4); 
    head = push(head, 8); 
    head = push(head, 12); 
    head = push(head, 10); 
 
    Console.WriteLine("Linked list before sorting:"); 
    printList(head); 
 
    // sort the linked list 
    head = sort(head); 
 
    Console.Write("\nLinked list after sorting:"); 
    printList(head); 
} 
} 
 
 
// This code is contributed by Princi Singh
 
  

Javascript

   <script>
// javascript implementation of recursive selection sort 
// for singly linked list | Swapping node links     // A Linked list node
     class Node {
        constructor(val) {
            this.data = val;
            this.next = null;
        }
    }
 
    // function to swap nodes 'currX' and 'currY' in a
    // linked list without swapping data
    function swapNodes(head_ref,  currX,  currY,  prevY) {
        // make 'currY' as new head
        head_ref = currY;
 
        // adjust links
        prevY.next = currX;
 
        // Swap next pointers
        var temp = currY.next;
        currY.next = currX.next;
        currX.next = temp;
        return head_ref;
    }
 
    // function to sort the linked list using
    // recursive selection sort technique
    function recurSelectionSort(head) {
        // if there is only a single node
        if (head.next == null)
            return head;
 
        // 'min' - pointer to store the node having
        // minimum data value
        var min = head;
 
        // 'beforeMin' - pointer to store node previous
        // to 'min' node
        var beforeMin = null;
        var ptr;
 
        // traverse the list till the last node
        for (ptr = head; ptr.next != null; ptr = ptr.next) {
 
            // if true, then update 'min' and 'beforeMin'
            if (ptr.next.data < min.data) {
                min = ptr.next;
                beforeMin = ptr;
            }
        }
 
        // if 'min' and 'head' are not same,
        // swap the head node with the 'min' node
        if (min != head)
            head = swapNodes(head, head, min, beforeMin);
 
        // recursively sort the remaining list
        head.next = recurSelectionSort(head.next);
 
        return head;
    }
 
    // function to sort the given linked list
    function sort(head_ref) {
        // if list is empty
        if ((head_ref) == null)
            return null;
 
        // sort the list using recursive selection
        // sort technique
        head_ref = recurSelectionSort(head_ref);
        return head_ref;
    }
 
    // function to insert a node at the
    // beginning of the 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 to the new node
        new_node.next = (head_ref);
 
        // move the head to point to the new node
        (head_ref) = new_node;
        return head_ref;
    }
 
    // function to print the linked list
    function printList(head) {
        while (head != null) {
            document.write(head.data + " ");
            head = head.next;
        }
    }
 
    // Driver code
     
        var head = null;
 
        // create linked list 10.12.8.4.6
        head = push(head, 6);
        head = push(head, 4);
        head = push(head, 8);
        head = push(head, 12);
        head = push(head, 10);
 
        document.write("Linked list before sorting:<br/>");
        printList(head);
 
        // sort the linked list
        head = sort(head);
 
        document.write("<br/>Linked list after sorting:<br/>");
        printList(head);
 
// This code is contributed by todaysgaurav 
</script>
 
  

Output

Linked list before sorting:n10 12 8 4 6  Linked list after sorting:n4 6 8 10 12

Time Complexity: O(n²)
Auxiliary Space: O(n)

Remove the common nodes in two Singly Linked Lists

GeeksforGeeks

Improve

Article Tags :

Practice Tags :

Recursive selection sort for singly linked list | Swapping node links

C++

Java

Python

C#

Javascript

Similar Reads