# GCD calculation using Euclidean algorithm fails

John Eipe

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Posts: 215

posted 7 years ago

Hi,

I have here a simple program to find the GCD - Greatest Common Divisor of 2 numbers using Euclidean algorithm. I guess that's the fastest way to compute GCD.

Here is the code:

I believe that the logic is correct. And i don't get any errors. But the output is always 0. (i.e., diff=0)

Please HELP!

I have here a simple program to find the GCD - Greatest Common Divisor of 2 numbers using Euclidean algorithm. I guess that's the fastest way to compute GCD.

Here is the code:

I believe that the logic is correct. And i don't get any errors. But the output is always 0. (i.e., diff=0)

Please HELP!

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pete stein

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John Eipe

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Peter Tellanaki

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Posts: 7

Peter Tellanaki

Greenhorn

Posts: 7

Campbell Ritchie

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John Eipe

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Posts: 215

Peter Tellanaki

Greenhorn

Posts: 7

posted 7 years ago

oh my,

i really nedd sleep !

forget all i said. your program will work if both numbers positive. if one positive one negative infinit loop. if both negative 0 always.

the way you use Euclid you must make certain both numbers are >0. but this is ok since +- no effect on gcd. so just sub first

x = Math.max(x, y); y = Math.min(x, y); with fx x = max of absolute values of x and y.

i really nedd sleep !

forget all i said. your program will work if both numbers positive. if one positive one negative infinit loop. if both negative 0 always.

the way you use Euclid you must make certain both numbers are >0. but this is ok since +- no effect on gcd. so just sub first

x = Math.max(x, y); y = Math.min(x, y); with fx x = max of absolute values of x and y.

Peter Tellanaki

Greenhorn

Posts: 7

posted 7 years ago

so for example

public class GCD {

public static void main(String[] args) throws IOException{

BufferedReader read = new BufferedReader(new InputStreamReader(System.in));

int diff=0;

System.out.println("Enter num1: ");

int x = Integer.parseInt(read.readLine());

System.out.println("Enter num2: ");

int y = Integer.parseInt(read.readLine());

x = Math.max(abs(x), abs(y));

y = Math.min(abs(x), abs(y));

[deleted]

System.out.print("GCD of the nums :"+diff);

}

private static int abs( int arg) {

return arg > 0 ? arg : -arg;

}

}

note: bad style with the static abs, but just to quick fix )

[edit]Delete solution. CR[/edit]

public class GCD {

public static void main(String[] args) throws IOException{

BufferedReader read = new BufferedReader(new InputStreamReader(System.in));

int diff=0;

System.out.println("Enter num1: ");

int x = Integer.parseInt(read.readLine());

System.out.println("Enter num2: ");

int y = Integer.parseInt(read.readLine());

x = Math.max(abs(x), abs(y));

y = Math.min(abs(x), abs(y));

[deleted]

System.out.print("GCD of the nums :"+diff);

}

private static int abs( int arg) {

return arg > 0 ? arg : -arg;

}

}

note: bad style with the static abs, but just to quick fix )

[edit]Delete solution. CR[/edit]

Ulf Dittmer

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Sridhar Santhanakrishnan

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Campbell Ritchie

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posted 7 years ago

Peter Tellanaki, I am very sorry (please don't be annoyed with me), but I have felt obliged to pull rank and delete part of your submission. If you look on the Beginner's Forum start page, it says

Simply providing the answer would prevent John Eipe from learning for himself.We're all here to learn, so when responding to others, please focus on helping them discover their own solutions, instead of simply providing answers.

posted 7 years ago

Exactly. You overwrite x with the maximum of x and y. Now if y is larger than x, x and y will end up having the same value.

Ulf Dittmer wrote:This is where the problem is:

x = Math.max(x, y);

y = Math.min(x, y);

Exactly. You overwrite x with the maximum of x and y. Now if y is larger than x, x and y will end up having the same value.

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John Eipe

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Posts: 215

John Eipe

Ranch Hand

Posts: 215

posted 7 years ago

Of course you can change that to the following, eliminating the empty body of the if-statement:

And I think Ulf would like some gratitude as well

And I think Ulf would like some gratitude as well

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