# Singly Linked List
A singly linked list is a type of linked list where each node stores a piece of data and a reference or pointer to the next node in the sequence. The last node in the list contains a null reference, indicating the end of the list.

## How To Create It
### Node
> Before we create the linked list we need to create the node of the linked list first like in singly linked list, we'll create a Node class with `data` and `next`

class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

### Singly Linked List
> Let's create our basic singly linked list without functionality

class SinglyLinkedList:
    def __init__(self):
        self.head = None

### Insert methods
> Let's implement insert method into it
> I want to insert at the beginning and the end
> This is how insert at the beginning look like
> 
> And this is how insert at the end look like
> 

def insert_at_beginning(self, data):
    # Create a new Node with data
    new_node = Node(data)

    # Checking if the linked list is empty
    if self.head is None:
        # If it is, we will put our new node into the head
        self.head = new_node
        return

    # If not, we will let next of the new node point to linked list
    new_node.next = self.head
    # And we will assign head of the linked list to our new node
    self.head = new_node

def insert_at_end(self, data):
    # Create a new Node with data
    new_node = Node(data)
    
    # Checking if the linked list is empty
    if self.head is None:
        # If it is, we will put our new node into the head
        self.head = new_node
        return

    # If not, we will store linked list into our variable
    # And looping to the end with it
    current_node = self.head
    # Checking til the end of the linked list
    while current_node.next is not None:
        current_node = current_node.next
        
    # We will assign next of the last node to our new node
    current_node.next = new_node

### Delete method
> After insert method we will implement delete method
> In this method it will delete the first value matchs with the condition
> This is how can we achieve it

def delete(self, data):
    # Checking if the linked list is empty
    if self.head is None:
        return

    # Checking if data delete match with the head of the linked list
    if self.head.data == data:
        # We will assign head of linked list to the next node
        self.head = self.head.next
        return

    # Storing previous node and current node
    # Previous node is the head node 
    # Because we already checked the head node 
    # So current node is the next node
    previous_node = self.head
    current_node = self.head.next

    # Looping til the end of the linked list
    while current_node is not None:
        # Checking if data is match with the current node
        if current_node.data == data:
            # If it is, we will point our previous node to next of the current node
            # Because we want to delete the current node
            previous_node.next = current_node.next
            return
        
        # Move to the next node
        # Assign previous node to current node 
        # And current node to next of the current node
        previous_node = current_node
        current_node = current_node.next

### Print Method

def __str__(self):
    # Checking if the linked list is empty
    if not self.head:
        return "List is empty"
    
    output = ""
    
    # Store current node before looping
    curr = self.head
    while curr:
        # Append current node's data to output variable with "->"
        output += str(curr.data) + "->"
        # Move to the next node
        curr = curr.next
    # Delete last "->" from output
    output = output[:-2]
    
    # Return output without leading and trailing whitespace
    return output.strip()

## Code

class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

class SinglyLinkedList:
    def __init__(self):
        self.head = None

    def insert_at_beginning(self, data):
        new_node = Node(data)

        if self.head is None:
            self.head = new_node
            return

        new_node.next = self.head
        self.head = new_node

    def insert_at_end(self, data):
        new_node = Node(data)

        if self.head is None:
            self.head = new_node
            return

        current_node = self.head
        while current_node.next is not None:
            current_node = current_node.next

        current_node.next = new_node

    def delete(self, data):
        if self.head is None:
            return

        if self.head.data == data:
            self.head = self.head.next
            return

        previous_node = self.head
        current_node = self.head.next

        while current_node is not None:
            if current_node.data == data:
                previous_node.next = current_node.next
                return

            previous_node = current_node
            current_node = current_node.next

    def __str__(self):
        if not self.head:
            return "List is empty"

        output = ""

        curr = self.head
        while curr:
            output += str(curr.data) + "->"
            curr = curr.next
        output = output[:-2]

        return output.strip()

## Example

def singly_linked_list_example():
    sll = SinglyLinkedList()

    # Insert Data
    sll.insert_at_beginning("Hello")
    sll.insert_at_beginning("World")

    sll.insert_at_end("World")

    # Print Linked List
    print(sll)  # World->Hello->World

    # Remove Data
    sll.delete("World")

    # Print Linked List
    print(sll)  # Hello->World

## GitHub

Code : [Singly Linked List](https://github.com/metaphorlism/data-structures/blob/main/linked_lists/SinglyLinkedList.py)

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