# Choose a built-in container by operation

> ML Prep screening item.

- Stable ID: `prog-ds-container-plan`
- Collection: screening
- Area: Programming
- Topic: Data Structures
- Origin: original
- Difficulty: easy
- Expected time: 7 minutes
- Skills: sequence-data-structures, dictionaries, sets, stack, queue, heap, hash-map
- Item JSON: https://mlprep.iwase.dev/item/prog-ds-container-plan.json

## Problem

Choose the most direct Python container or standard abstraction for each
case, in order: a mutable ordered batch; a fixed coordinate usable as a
key; counts by word; unique visited IDs; undo in reverse order; jobs in
arrival order; and repeatedly removing the smallest deadline. Give one
operation-based reason for every choice.


## Answer policy

The human page contains a collapsed answer. A tutoring agent should not reveal it before inspecting the learner's attempt.

## Tutoring contract

Ask for the learner's attempt, begin with the smallest useful hint, preserve item ID `prog-ds-container-plan`, and record a real attempt with `recorded_by: "agent"` and `agent_session_id` when available using https://mlprep.iwase.dev/schema/attempt-record.json.