What is the difference between HashMap and LinkedList?

HashMap

• Implements an associative array (key-value map).
• Access, insertion, and deletion of elements have an average complexity of O(1).
• The order of elements is not guaranteed.
• Uses hashing for fast lookup.

// Example of using HashMap
import 'dart:collection';

void main() {
  final HashMap<String, int> inventory = HashMap();
  inventory['apples'] = 5;
  inventory['bananas'] = 10;
  print(inventory['apples']); // Will output 5
}

LinkedList

• Implements a linked list.
• Access to an element by index has a complexity of O(n).
• Insertion and deletion at the beginning or end of the list have a complexity of O(1).
• Efficient for operations involving adding/removing elements anywhere in the list (with a node reference) with a complexity of O(1).
• Supports insertion and deletion of elements while maintaining node references (LinkedListEntry), ensuring O(1).
• The order of elements corresponds to the order of addition.

// Example of using LinkedList
import 'dart:collection';

void main() {
  final LinkedList<String> shoppingList = LinkedList();
  shoppingList.addFirst(LinkedListEntry('Milk'));
  shoppingList.add(LinkedListEntry('Bread')); // Adds to the end
  print(shoppingList.first); // Will output Milk
  print(shoppingList.where((entry) => entry.element == 'Bread').first.element); // Example of access, not optimal
}

// Example of using LinkedListEntry
class LinkedListEntry<T> extends LinkedListEntry<LinkedListEntry> {
  final T data;
  LinkedListEntry(this.data);

  @override
  String toString() => data.toString();
}

Characteristic	HashMap	LinkedList
Data structure	Associative array	Linked list
Storage	Key-value pairs	Elements (nodes)
Index access	Not supported directly	O(n)
Key access	O(1) on average	Not supported
Insertion/Deletion	O(1) on average	O(1) at start/end, O(1) via node reference
Element order	Not guaranteed	Preserves insertion order
Memory usage	Higher due to hashing	Less if nodes are small
Main purpose	Fast key-based lookup	Efficient operations at start/end/any part (via reference)