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.
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 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 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# 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
<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>
OutputLinked 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)
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