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This is a medium difficulty Coding & Algorithms question, commonly asked during trading - 网上海投 - 在线笔试 rounds at Hudson River Trading.

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This question is commonly asked for Software Engineer candidates at Hudson River Trading during technical interviews.

Count Length-3 Chat Substrings with a Vowel | Hudson River Trading Coding Question

Quick Overview

This Hudson River Trading coding question checks careful string scanning over fixed-length substrings with a small character predicate. It is a compact console-ready exercise for practicing boundary handling, linear traversal, and turning a short interview prompt into reliable code.

Quick Overview

Count Length-3 Chat Substrings with a Vowel

Company: Hudson River Trading

Role: Software Engineer

Category: Coding & Algorithms

Difficulty: medium

Interview Round: trading - 网上海投 - 在线笔试

You are developing an automatic moderation system for a chat application that detects simple linguistic patterns. Given a string `chatMessage`, count how many substrings of exactly length `3` contain at least one vowel. Vowels are `a`, `e`, `i`, `o`, and `u`, and uppercase vowels should count as vowels too. Return the count as an integer. Example 1: ```text chatMessage = "codeSignal" output = 8 ``` The length-3 substrings are `cod`, `ode`, `des`, `esi`, `sig`, `ign`, `gna`, and `nal`; each contains at least one vowel. Example 2: ```text chatMessage = "StrEngThen" output = 5 ``` Among the eight length-3 substrings, five contain at least one vowel. Constraints: - `0 <= chatMessage.length <= 100000` - `chatMessage` contains English letters. - A solution with worse than linear time is acceptable for small inputs, but aim for a simple linear scan.

Quick Answer: This Hudson River Trading coding question checks careful string scanning over fixed-length substrings with a small character predicate. It is a compact console-ready exercise for practicing boundary handling, linear traversal, and turning a short interview prompt into reliable code.

Given a string chatMessage, count substrings of exactly length 3 that contain at least one vowel. Vowels are a, e, i, o, u and uppercase variants.

Constraints

0 <= chatMessage.length <= 100000
chatMessage contains English letters.

Examples

Input: ("codeSignal",)

Expected Output: 8

Explanation: Every length-3 window contains a vowel.

Input: ("StrEngThen",)

Expected Output: 5

Explanation: Five of the eight windows contain a vowel.

Input: ("",)

Expected Output: 0

Input: ("ab",)

Expected Output: 0

Input: ("bcdf",)

Expected Output: 0

Input: ("aaa",)

Expected Output: 1

Input: ("ABC",)

Expected Output: 1

Input: ("bcAxyz",)

Expected Output: 3

Input: ("rhythm",)

Expected Output: 0

Hints

Scan each window of length 3.
Uppercase vowels count too.
Strings shorter than 3 have no valid substrings.

Last updated: Jul 2, 2026

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