How do you implement a stack using a linked list?

You can implement a stack using a linked list by treating the head of the list as the top of the stack.

A stack is a data structure that follows the Last-In-First-Out (LIFO) principle. This means that the last element added to the stack will be the first one to be removed. In the context of a linked list, this translates to adding and removing elements from the head of the list, which is the most efficient operation in a linked list.

To implement a stack using a linked list, you would need to define a Node class and a Stack class. The Node class would have two properties: 'data', to store the value of the node, and 'next', to point to the next node in the list. The Stack class would have a 'head' property to keep track of the top of the stack, and methods for the stack operations: 'push', 'pop', and 'peek'.

The 'push' method would add a new node to the head of the list. It would create a new node with the given value, set its 'next' property to the current head of the list, and then update the head of the list to the new node.

The 'pop' method would remove the node at the head of the list and return its value. It would store the value of the current head, update the head to the next node in the list, and then return the stored value. If the list is empty, it would return null or throw an exception, depending on your preference.

The 'peek' method would return the value of the node at the head of the list without removing it. It would simply return the value of the current head. If the list is empty, it would return null or throw an exception, just like the 'pop' method.

In this way, you can use a linked list to implement a stack with efficient O(1) operations. Remember, the key is to treat the head of the list as the top of the stack, and to add and remove elements from the head of the list.