Topic: Linked Lists in Python – Part 2: Insertion, Deletion, and Search Operations

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Recap from Part 1

• A singly linked list consists of nodes, where each node holds data and a pointer to the next node.

• We've implemented basic append and display functions.

Now we’ll explore insertion at specific positions, deletion, and searching.

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1. Insert at a Specific Position

def insert_at_position(self, index, data):
    if index < 0:
        raise IndexError("Index cannot be negative")
    
    new_node = Node(data)
    
    if index == 0:
        new_node.next = self.head
        self.head = new_node
        return

    current = self.head
    for _ in range(index - 1):
        if not current:
            raise IndexError("Index out of bounds")
        current = current.next
    
    new_node.next = current.next
    current.next = new_node

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2. Delete a Node by Value

def delete_by_value(self, value):
    if not self.head:
        return

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

    current = self.head
    while current.next and current.next.data != value:
        current = current.next

    if current.next:
        current.next = current.next.next

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3. Delete a Node by Index

def delete_by_index(self, index):
    if index < 0:
        raise IndexError("Index cannot be negative")

    if not self.head:
        raise IndexError("List is empty")

    if index == 0:
        self.head = self.head.next
        return

    current = self.head
    for _ in range(index - 1):
        if not current.next:
            raise IndexError("Index out of bounds")
        current = current.next

    if current.next:
        current.next = current.next.next

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4. Search for an Element

def search(self, value):
    current = self.head
    index = 0
    while current:
        if current.data == value:
            return index
        current = current.next
        index += 1
    return -1  # Not found

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5. Complete Class with All Methods

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

    def append(self, data): ...
    def display(self): ...
    def insert_at_position(self, index, data): ...
    def delete_by_value(self, value): ...
    def delete_by_index(self, index): ...
    def search(self, value): ...

*(You can reuse the method definitions above.)*

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Summary

• You can manipulate linked lists with insertions and deletions at any position.

• Searching through a singly linked list is O(n).

• Always check for edge cases: empty list, index bounds, and duplicates.

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Exercise

• Write a method reverse() that reverses the linked list in-place and test it on a list of 5+ elements.

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#DSA #LinkedList #Python #Insertion #Deletion #Search

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