C++ Program For Recursive Selection Sort For Singly Linked List – Swapping Node Links
Last Updated :
30 Mar, 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.
C++
#include <bits/stdc++.h>
using namespace std;
struct Node
{
int data;
struct Node* next;
};
void swapNodes(struct Node** head_ref,
struct Node* currX,
struct Node* currY,
struct Node* prevY)
{
*head_ref = currY;
prevY->next = currX;
struct Node* temp = currY->next;
currY->next = currX->next;
currX->next = temp;
}
struct Node* recurSelectionSort(struct Node* head)
{
if (head->next == NULL)
return head;
struct Node* min = head;
struct Node* beforeMin = NULL;
struct Node* ptr;
for (ptr = head; ptr->next != NULL;
ptr = ptr->next)
{
if (ptr->next->data < min->data)
{
min = ptr->next;
beforeMin = ptr;
}
}
if (min != head)
swapNodes(&head, head, min, beforeMin);
head->next = recurSelectionSort(head->next);
return head;
}
void sort(struct Node** head_ref)
{
if ((*head_ref) == NULL)
return;
*head_ref = recurSelectionSort(*head_ref);
}
void push(struct Node** head_ref,
int new_data)
{
struct Node* new_node =
(struct Node*)malloc(sizeof(struct Node));
new_node->data = new_data;
new_node->next = (*head_ref);
(*head_ref) = new_node;
}
void printList(struct Node* head)
{
while (head != NULL)
{
cout << head->data << " ";
head = head->next;
}
}
int main()
{
struct Node* head = NULL;
push(&head, 6);
push(&head, 4);
push(&head, 8);
push(&head, 12);
push(&head, 10);
cout <<
"Linked list before sorting:n";
printList(head);
sort(&head);
cout <<
"Linked list after sorting:n";
printList(head);
return 0;
}
|
Output:
Linked list before sorting:
10 12 8 4 6
Linked list after sorting:
4 6 8 10 12
Time Complexity: O(n2)
Auxiliary Space: O(n)
Please refer complete article on Recursive selection sort for singly linked list | Swapping node links for more details!
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