LeetCode-Style Stack Design Round

EasyPython

Problem

Arista EOS components often process temporary command or event state in last-in, first-out order. Design a stack abstraction that stores generic elements and supports standard operations efficiently.

Implement stack_operations(operations), which receives a sequence of commands and returns the results produced by query commands. Internally, define a stack that stores values without assuming a specific element type.

Formal Specification

Each operation is a list whose first item is a command:

['push', value]: Add value to the top of the stack. This produces no result.
['pop']: Remove and return the top value. Return None if the stack is empty.
['peek']: Return the top value without removing it. Return None if the stack is empty.
['size']: Return the number of stored elements.
['is_empty']: Return True when the stack has no elements, otherwise False.

Return a list containing results from pop, peek, size, and is_empty commands in their original order. Values may be integers, strings, or booleans, and pushed values are never None.

Constraints

1 <= len(operations) <= 10^5
Each operation is valid and has the required number of items.
At most 10^5 values are stored over the execution.
Every pushed value is an integer, string, or boolean, and is not None.

Function Signature

def stack_operations(operations):

Arista EOS components often process temporary command or event state in last-in, first-out order. Design a stack abstraction that stores generic elements and supports standard operations efficiently.

Formal Specification

Each operation is a list whose first item is a command:

['push', value]: Add value to the top of the stack. This produces no result.
['pop']: Remove and return the top value. Return None if the stack is empty.
['peek']: Return the top value without removing it. Return None if the stack is empty.
['size']: Return the number of stored elements.
['is_empty']: Return True when the stack has no elements, otherwise False.

Return a list containing results from pop, peek, size, and is_empty commands in their original order. Values may be integers, strings, or booleans, and pushed values are never None.