# Bubble Sort for Linked List by Swapping Nodes ### Introduction

The linked list is one of the most important concepts and data structures to learn while preparing for interviews. Having a good grasp of Linked Lists can be a huge plus point in a coding interview.

### Problem Statement

In this problem, we are given a singly linked list. We have to sort this list using bubble sort.

Note: The bubble sort will be applied on nodes instead of values i.e., We have to swap the nodes instead of values.

### Problem Statement Understanding

Let’s try to understand the problem statement with the help of examples by referring the best websites to learn coding.

Suppose the given list is 5 → 1 → 4 → 2 → 8.

• According to the problem statement, we have to sort the given list using bubble sort.
• What do we usually do? We usually swap the node data. But here, we have to swap the nodes and not their data.
• In the first step, suppose we have to swap 5 and 1. So, we will swap the nodes and not their data. So, the linked list after the first step will be 1 → 5 → 4 → 2 → 8. In this way, swapping will happen, and our final sorted linked list will be 1 → 2 → 4 → 5 → 8

Input: Output: Explanation: As we can see, the given singly linked list has been sorted.

This question is not a very complex one. We have to apply a normal bubble sort on the list. The only difference is that instead of swapping the data of adjacent nodes, we will swap the nodes. Let us have a glance at the approach.

### Swap() function

In the swap() function, we will see how we can swap two adjacent nodes.

• Let the two adjacent nodes be p1 and p2.
• Now we will create 2 pointers ptr1 and ptr2, and will make ptr1 point to p1 and ptr2 point to p2.
• Next, we will create a pointer temp, and will make it point to the next of ptr2.
• We will make the next of ptr2 point to ptr1 and next of ptr1 point to temp.
• In this way, following the above steps, the two adjacent nodes p1 and p2 will get swapped.

### Dry Run (Swap() function) ### BubbleSort()

In this method, we will see how to perform Bubble Sort on the linked list.

• First, we need the count of the number of nodes in the list. The count can be found with a single list traversal.
• Now, the first loop is going to run from 0 to count-1.
• Inside the first loop, we will create a node pointer h that will point to the head and a variable swapped, initializing it with 0.
• The nested loop will run from 0 to count-i-1.
• Inside the nested loop, we will check if the adjacent elements are following ascending order or not.
• If any pair of adjacent nodes are not following the ascending order, we will swap the nodes and the value of swapped will become 1.
• After the above, if condition, we will increment the h.
• Now, after the inner loop, if the value of the variable swapped remains 0, it means that the list is sorted, and we will break the loop. Otherwise we will continue with the loop.

### Dry Run (Bubble sort)   ### Code Implementation

```#include <stdio.h>
#include <stdlib.h>

/* structure for a node */
struct Node {
int data;
struct Node* next;
} Node;

/*Function to swap the nodes */
struct Node* swap(struct Node* ptr1, struct Node* ptr2)
{
struct Node* tmp = ptr2->next;
ptr2->next = ptr1;
ptr1->next = tmp;
return ptr2;
}

/* Function to sort the list */
int bubbleSort(struct Node** head, int count)
{
struct Node** h;
int i, j, swapped;

for (i = 0; i <= count; i++) {

swapped = 0;

for (j = 0; j < count - i - 1; j++) {

struct Node* p1 = *h;
struct Node* p2 = p1->next;

if (p1->data > p2->data) {

/* update the link after swapping */
*h = swap(p1, p2);
swapped = 1;
}

h = &(*h)->next;
}

/* break if the loop ended without any swap */
if (swapped == 0)
break;
}
}

/* Function to print the list */
void printList(struct Node* n)
{
while (n != NULL) {
printf("%d -> ", n->data);
n = n->next;
}
printf("\n");
}

/* Function to insert a struct Node
at the beginning of a linked list */
void insertAtTheBegin(struct Node** start_ref, int data)
{
struct Node* ptr1
= (struct Node*)malloc(sizeof(struct Node));

ptr1->data = data;
ptr1->next = *start_ref;
*start_ref = ptr1;
}

// Driver Code
int main()
{
int arr[] = { 78, 20, 10, 32, 1, 5 };
int list_size, i;

struct Node* start = NULL;
list_size = sizeof(arr) / sizeof(arr);

/* Create linked list from the array arr[] */
for (i = 0; i < list_size; i++)
insertAtTheBegin(&start, arr[i]);

/* print list before sorting */
printList(start);

/* sort the linked list */
bubbleSort(&start, list_size);

/* print list after sorting */
printList(start);

return 0;
}
```
```#include <iostream>
using namespace std;

struct Node
{
int data;
struct Node* next;
} Node;

struct Node* swap(struct Node* ptr1, struct Node* ptr2)
{
struct Node* tmp = ptr2->next;
ptr2->next = ptr1;
ptr1->next = tmp;
return ptr2;
}

int bubbleSort(struct Node** head, int count)
{
struct Node** h;
int i, j, swapped;

for (i = 0; i <  count; i++)
{

swapped = 0;

for (j = 0; j < count  - i -1; j++)
{

struct Node* p1 = *h;
struct Node* p2 = p1->next;

if (p1->data > p2->data)
{

*h = swap(p1, p2);
swapped = 1;
}

h = &(*h)->next;
}

if (swapped == 0)
break;
}
}

void printList(struct Node* n)
{
while (n != NULL)
{
cout << n->data << " -> ";
n = n->next;
}
cout << endl;
}

void insertAtTheBegin(struct Node** start_ref, int data)
{
struct Node* ptr1
= (struct Node*)malloc(sizeof(struct Node));

ptr1->data = data;
ptr1->next = *start_ref;
*start_ref = ptr1;
}

int main()
{
int arr[] = { 8, 2, 4, 1, 5 };
int list_size, i;

struct Node* start = NULL;
list_size = sizeof(arr) / sizeof(arr);

for (i = 0; i < list_size; i++)
insertAtTheBegin(&start, arr[i]);

printList(start);

bubbleSort(&start, list_size);

printList(start);

return 0;
}
```
```
//By using get higher node

static class Node {
int data;
Node next;
}
//Class constructors
}
//insert element
public void insert(int value) {
//Create  node
Node node = new Node();
node.data = value;
node.next = null;
else {
//find last node
while (temp.next != null) {
temp = temp.next;
}
temp.next = node;
}

}
public void display() {

while (temp != null) {
System.out.print("  " + temp.data);
temp = temp.next;
}
} else {
}
}
//perform bubble sort in single linked list
public void bubbleSort() {

Node current = null,
move_node = null,
prev = null;

prev = null;
while (current != null) {

//When current node value is grator than previous node
if (current.next != null && current.next.data > move_node.data) {
//Swap node values
move_node = current.next;
prev = current;

}
current = current.next;
}
}

if (prev != null) {
prev.next = move_node.next;
}
}

} else {
}
}

public static void main(String[] args) {

obj.insert(7);
obj.insert(50);
obj.insert(9);
obj.insert(42);
obj.insert(5);
obj.insert(15);
System.out.print("Before sort : ");

//display all node
obj.display();

obj.bubbleSort();
System.out.print("\nAfter sort  : ");

obj.display();
}
}
```
```
#By using get higher node
class Node:
def __init__(self,data):
self.data=data
self.next=None

def __init__(self):
#Assign default value

#insert new node to linked list
def insert(self,data):
node=Node(data)
node.next=None
else:
while temp.next!=None:
temp=temp.next
temp.next=node

def display(self):
return

while(temp!=None):
print(temp.data,end=" ")
temp=temp.next

#perform bubble sort in single linked list
def bubbleSort(self):

current=None
move_node=None
prev=None

prev=None
while(current!=None):

#When current node value is grator than previous node
if(current.next!=None and  current.next.data>move_node.data):
#Swap node values
move_node=current.next
prev=current

current=current.next

if(prev!=None):
prev.next=move_node.next

else:

def main():
obj.insert(7)
obj.insert(50)
obj.insert(9)
obj.insert(42)
obj.insert(5)
obj.insert(15)
print("Before sort : ")

#display all node
obj.display()

obj.bubbleSort()
print("\nAfter sort  : ")

obj.display()
if __name__=="__main__":
main()
```