Recursive selection sort for singly linked list | Swapping node links
Given a singly linked list containing n nodes. The problem is to sort the list using recursive selection sort technique. The approach should be such that it involves swapping node links instead of swapping nodes data.
Examples:
Input : 10 -> 12 -> 8 -> 4 -> 6 Output : 4 -> 6 -> 8 -> 10 -> 12
In Selection Sort, we first find minimum element, swap it with the beginning node and recur for remaining list. Below is recursive implementation of these steps for 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 is modified accordingly for the implementation of this post.
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 |
Output:
Linked list before sorting: 10 12 8 4 6 Linked list after sorting: 4 6 8 10 12
Time Complexity: O(n2)
This article is contributed by Ayush Jauhari. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.
