doubly_LL.py

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

class DoublyLinkedList:
    def __init__(self, value):
        new_node = Node(value)
        self.head = new_node
        self.tail = new_node
        self.length = 1 # Keeping track of length is very helpful for edge cases!

    def print_list(self):
        temp = self.head
        while temp is not None:
            print(temp.value)
            temp = temp.next

    def append(self, value):
        new_node = Node(value)
        if self.head is None:
            self.head = new_node
            self.tail = new_node
        else:
            self.tail.next = new_node
            new_node.prev = self.tail
            self.tail = new_node
        self.length += 1
        return True

    def pop(self):
        if self.length == 0: # Check length instead of head is None (cleaner)
            return None
        
        temp = self.tail
        if self.length == 1: # EDGE CASE FIX: List has only 1 item
            self.head = None
            self.tail = None
        else:
            self.tail = self.tail.prev
            self.tail.next = None
            temp.prev = None
            
        self.length -= 1
        return temp

    def prepend(self, value):
        new_node = Node(value)
        if self.length == 0:
            self.head = new_node
            self.tail = new_node
        else:
            new_node.next = self.head
            self.head.prev = new_node
            self.head = new_node
        self.length += 1
        return True

    def pop_first(self):
        if self.length == 0:
            return None
        
        temp = self.head
        if self.length == 1: # EDGE CASE FIX: List has only 1 item
            self.head = None
            self.tail = None
        else:
            self.head = self.head.next
            self.head.prev = None
            temp.next = None
            
        self.length -= 1
        return temp

    def get(self, index):
        # FIX: Validate index against length
        if index < 0 or index >= self.length: 
            return None
        
        # Optimization: Start from tail if index is in the second half!
        if index < self.length / 2:
            temp = self.head
            for _ in range(index):
                temp = temp.next
        else:
            temp = self.tail
            for _ in range(self.length - 1, index, -1):
                temp = temp.prev
                
        return temp # FIX: Return the NODE, not the value

    def set_value(self, value, index):
        temp = self.get(index)
        if temp:
            temp.value = value
            return True
        return False

    def insert(self, value, index):
        if index < 0 or index > self.length:
            return False
        if index == 0:
            return self.prepend(value)
        if index == self.length: # FIX: Handle inserting at the very end
            return self.append(value)

        new_node = Node(value)
        before = self.get(index - 1)
        after = before.next

        new_node.prev = before
        new_node.next = after
        before.next = new_node
        after.prev = new_node
        
        self.length += 1
        return True

    def remove(self, index):
        if index < 0 or index >= self.length:
            return None # Changed return False to return None (standard for remove)
        
        if index == 0:
            return self.pop_first() # FIX: Added parentheses
        if index == self.length - 1: # FIX: Handle removing the last item
            return self.pop()

        temp = self.get(index)
        
        temp.prev.next = temp.next
        temp.next.prev = temp.prev
        
        temp.next = None
        temp.prev = None

        self.length -= 1
        return temp