Custom Stack or Queue

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Your question is Custom Stack or Queue. Start with the requirements on the right.

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Problem

How would you implement a custom stack or queue using basic arrays or linked lists?

Implement process_operations(mode, operations), where mode is either "stack" or "queue". Each operation is an array such as ["push", value], ["pop"], ["enqueue", value], or ["dequeue"]. Return the values produced by removal and peek operations in order. Return None for removal or peek operations on an empty structure.

Use a custom implementation rather than Python's built-in queue classes. The structure should support constant-time insertion, removal, and peek operations.

Constraints

mode is either "stack" or "queue"
1 <= operations.length <= 10^4
Each operation is valid for the selected mode
Values may be integers, strings, or null
An empty pop, dequeue, or peek returns None

Function Signature

def process_operations(mode, operations):

Your solutionPython 3

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