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Thread: Odd and Even Numbers

  1. #1
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    Question [SOLVED] Odd and Even Numbers

    I am trying to create an "algorithm" (what I have now really isn't), I just can't seem to wrap my head around the concept, or on how to do this.. Here is the monstrosity I have created so far:

    package org.buchanan.math;
     
    import java.util.ArrayList;
    import java.util.List;
     
    public class Numbers {
     
    	private List<Integer> oddNumbers = new ArrayList<Integer>();
    	private List<Integer> evenNumbers = new ArrayList<Integer>();
     
    	public void populateLists() {
    		for (int j = 0; j < Integer.MAX_VALUE; j += 1) {
    			this.oddNumbers.add(j);
    			System.out.println(j);
    		}
    		System.out.println("Odd numbers added!");
    		for (int i = 0; i < Integer.MAX_VALUE; i += 2) {
    			this.evenNumbers.add(i);
    		}
    		System.out.println("Even numbers added!");
    	}
     
    	public boolean isOddNumber(int n) {
    		return this.oddNumbers.contains(n) ? true : false;
    	}
     
    	public boolean isEvenNumber(int n) {
    		return this.evenNumbers.contains(n) ? true : false;
    	}
    }

    As you see, this destroys my memory, is slow as all get out, and not efficient in any way. Anybody have any suggestions on how to make this? Maybe even somewhere easier to start learning things like this?
    Last edited by tyb97; September 30th, 2012 at 04:31 PM. Reason: Thanks


  2. #2
    Super Moderator helloworld922's Avatar
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    Default Re: Odd and Even Numbers

    Try using the Modulo operator. It will save you a lot of time and memory.

  3. The Following User Says Thank You to helloworld922 For This Useful Post:

    tyb97 (September 30th, 2012)

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    Default Re: Odd and Even Numbers

    Quote Originally Posted by helloworld922 View Post
    Try using the Modulo operator. It will save you a lot of time and memory.
    Ahh, thanks a ton. I still don't fully understand them, but in time I will. I was able to reduce my code from the above to this:

    package org.buchanan.math;
     
    public class Numbers {
     
    	public boolean isOddNumber(int n) {
    		return n % 2 != 0 ? true : false;
    	}
     
    	public boolean isEvenNumber(int n) {
    		return n % 2 == 0 ? true : false;
    	}
    }

    Which really helps a ton, and save a lot of memory.

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    Super Moderator Norm's Avatar
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    Default Re: Odd and Even Numbers

    return n % 2 != 0 ? true : false;
    You could return the results of the != directly and not need to use the ternary statement.
    return n % 2 != 0;
    If you don't understand my answer, don't ignore it, ask a question.

  6. The Following User Says Thank You to Norm For This Useful Post:

    tyb97 (September 30th, 2012)

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    Default Re: Odd and Even Numbers

    Quote Originally Posted by Norm View Post
    You could return the results of the != directly and not need to use the ternary statement.
    return n % 2 != 0;
    I see. Thank you for the kind insight.

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