Seriously Good Software: Code that works, survives, and wins by Marco Faella

Author:Marco Faella
Language: eng
Format: mobi, epub, pdf
Publisher: Manning Publications
Published: 2020-03-16T10:06:57.356000+00:00

1 The original procedure goes here (modifies u and v).

int gcd = -u * ( 1 <{}< k);

assert isGcd(gcd, originalU, originalV) : "Wrong GCD!";

return gcd;

}

For the auxiliary isGcd method, I said the simplest solution is preferable. In this case, you may simply apply the definition of “greatest common divisor,” and check that

gcd is indeed a common divisor of originalU and originalV

every larger number is not a common divisor

private static boolean isGcd(int gcd, int u, int v) {

if (u \% gcd != 0 || v \% gcd != 0) 1 Checks that gcd is a common divisor

return false;

for (int i=gcd+1; i<=u && i<=v; i++) 2 Checks any larger number,

if (u \% i == 0 && v \% i == 0) up to the minimum of u and v

return false;

return true;

}

This implementation of isGcd is very inefficient, being linear in the size of the smallest number between u and v. A more reasonable course of action would be to use Euclid’s classic algorithm (https://en.wikipedia.org/wiki/Euclidean_algorithm) or invoke an already implemented GCD procedure, such as the BigInteger.gcd() method from the JDK.

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