The Counting Machine

A medium Python interview practice problem on DataDriven. Write and execute real python code with instant grading.

Domain

Python

Difficulty

medium

Seniority

L4

Problem

Implement the iterator class `CountUp(values)` and the top-level driver `count_up(values)`. `CountUp` is a stateful iterator: iterating over it yields `values[i] * (i + 1)` for `i = 0 .. len(values) - 1` (1-based multiplier). It must implement the iterator protocol: `__iter__` returns the iterator and `__next__` produces the next transformed value, raising `StopIteration` once the values are exhausted. The test harness calls `count_up(values)`, where `values` is a list of integers. Construct a `CountUp` over `values`, drive it to completion (equivalent to `list(iter(CountUp(values)))`), and return the resulting list of integers in order. For an empty `values`, return an empty list `[]`.

Summary

It knows where it stopped last time.

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