arrays - What is the top of the stack in various stack implementation? -

when implementing stack, element stack's top?

• stack implemented linked list
• stack implemented array

stack implemented linked list

in implementation, have linked list, , pointer/reference first element of list. element top of stack.

• when want add element, create new node, link current head, , modify head new element. push(x) in stack.
• when pop() element, take head, set new head following element, , return value of old head.

both operations done in constant time.

stack implemented array

when implementing stack array, circular array implementation. means if array of length n, refer element @ index 0 , 1 @ index n-1 adjacent.

in implementation, hold index of "top" of stack, , modify whenever pop or push elements stack. top of stack not in constant index in implementation.