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Group Words by First Letter

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Ever had a massive list of data and wished you could instantly organize it into neat, labeled folders? That’s exactly what this challenge is about! You’re going to master Java Collectors, specifically the groupingBy operation. Your mission is to take a stream of words and aggregate them into a Map where they’re organized by their first letter.

The "secret sauce" here is the power of the Stream API. Instead of writing manual loops and initializing empty lists, Collectors.groupingBy does all the heavy lifting in a single, readable pass. Think of it like an automated sorting machine: as each word flies by, the machine looks at the first letter and tosses it into the correct bucket. It’s incredibly efficient, elegant, and avoids the boilerplate code that usually litters data aggregation tasks.

This is a fundamental skill for data analysis and reporting in modern Java. Mastering collectors allows you to transform complex streams into structured data with just a few lines of code!

If sorting is part of the strategy, do it intentionally as a preprocessing step to simplify downstream logic such as merging, ordering, or comparison. After sorting, keep output semantics precise: preserve expected structure, avoid dropping valid entries, and ensure tied cases still follow deterministic order rules.

Algorithm Flow

Recommendation Algorithm Flow for Group Words by First Letter - Budibadu
Recommendation Algorithm Flow for Group Words by First Letter - Budibadu

Best Answers

java - Approach 1
import java.util.*;
import java.util.stream.Collectors;

class Solution {
    public Map<Character, List<String>> groupWords(List<String> words) {
        return words.stream()
                   .collect(Collectors.groupingBy(
                       word -> word.charAt(0),
                       Collectors.toList()
                   ));
    }
}