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Add Modular Arithmetic approach to RaindropConverter #3144

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Add Modular Arithmetic approach to RaindropConverter
habere-et-dispertire Jun 22, 2026
c5802d2
Refactor RaindropConverter default case
habere-et-dispertire Jun 23, 2026
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27 changes: 27 additions & 0 deletions exercises/practice/raindrops/.approaches/introduction.md
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Expand Up @@ -54,6 +54,32 @@ class RaindropConverter {

For more information, check the [`Map` approach][approach-map].

## Approach: `Modular Arithmetic`

```java
import java.math.BigInteger;

@kahgoh kahgoh Jun 23, 2026

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Formatting

Suggested change
import java.math.BigInteger;
import java.math.BigInteger;

import static java.math.BigInteger.valueOf;

class RaindropConverter {

String convert (int n) {
switch ( valueOf(n).modPow( valueOf(12), valueOf(105) ).intValue() ) {
case (36): { return "Pling"; }
case (85): { return "Plang"; }
case (91): { return "Plong"; }
case (15): { return "PlingPlang"; }
case (21): { return "PlingPlong"; }
case (70): { return "PlangPlong"; }
case ( 0): { return "PlingPlangPlong"; }
default : { return String.valueOf(n); }
}
}

}
```

For more information, check the [`Modular arithmetic` approach][approach-modular].

@kahgoh kahgoh Jun 23, 2026

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The linked page describes the problem differently. It might be confusing because the page starts with "Fizz Buzz" instead and then generalizes the problem - it doesn't describe it in the same terms as the exercise. I think it might help to state the that the problem is like "Fizz" & "Buzz" and that the Modular arithmetic approach can be used to solve this type of problem.


## Which approach to use?

Benchmarking with the [Java Microbenchmark Harness][jmh] is currently outside the scope of this document,
Expand All @@ -64,4 +90,5 @@ and no other code would need to be added.
[remainder-operator]: https://www.geeksforgeeks.org/modulo-or-remainder-operator-in-java/
[approach-if-statements]: https://exercism.org/tracks/java/exercises/raindrops/approaches/if-statements
[approach-map]: https://exercism.org/tracks/java/exercises/raindrops/approaches/map
[approach-modular]: https://philcrissman.net/posts/eulers-fizzbuzz/
[jmh]: https://github.com/openjdk/jmh