Which data structure can be used to implement both stack and queue (only one data structure)

A linked list can be used to implement both a stack and a queue.

For a stack, you can use the linked list by adding and removing elements from the head of the list. This way, the last element added (the one at the head of the list) will be the first one to be removed, following the LIFO (Last In, First Out) principle of a stack.

For a queue, you can also use the linked list by adding elements at the tail of the list and removing them from the head. This way, the first element added (the one at the head of the list) will be the first one to be removed, following the FIFO (First In, First Out) principle of a queue.

So, a linked list can be used to implement both a stack and a queue, depending on how you add and remove elements.