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This question is commonly asked for Machine Learning Engineer candidates at Anthropic during technical interviews.

Convert State Stream to Events | Anthropic Coding Question

Quick Overview

This question evaluates a candidate's ability to process sequential categorical data by identifying and summarizing consecutive runs, reason about time and space complexity, and apply length-based filtering of events.

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Part 2: Convert State Stream into Events with Minimum Run Length

You are given a list `states` where `states[i]` is the categorical output of a monitoring function at timestamp `i`. Consecutive equal values form a run. Given an integer `k`, return only those events whose run length is at least `k`. Each valid event should be represented as `(value, start_index, end_index)`, using inclusive 0-based indices. Important: short runs are simply discarded. They do not merge neighboring runs, even if the neighboring runs have the same value. Example: `states = ['A', 'A', 'B', 'B', 'B', 'A']`, `k = 2` should return `[('A', 0, 1), ('B', 2, 4)]`.

Constraints

0 <= len(states) <= 100000
1 <= k <= 100000
Each element in `states` supports equality comparison
Runs are determined from the original stream before filtering

Examples

Input: (['A', 'A', 'B', 'B', 'B', 'A'], 2)

Expected Output: [('A', 0, 1), ('B', 2, 4)]

Explanation: The final A run has length 1, so it is excluded.

Input: (['A', 'A', 'B', 'A', 'A'], 2)

Expected Output: [('A', 0, 1), ('A', 3, 4)]

Explanation: The middle B run is too short and is removed, but the two A runs are not merged because they were separated in the original stream.

Input: ([], 1)

Expected Output: []

Explanation: An empty stream produces no events.

Input: (['X'], 1)

Expected Output: [('X', 0, 0)]

Explanation: A single-element run is valid when k = 1.

Input: (['A', 'B', 'B', 'C', 'C', 'C', 'D'], 3)

Expected Output: [('C', 3, 5)]

Explanation: Only the C run has length at least 3.

Hints

First identify each consecutive run exactly as in Part 1.
Before appending a run, compute its length as `end_index - start_index + 1` and compare it with `k`.

Quick Overview