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Collection exercise Scrabble

Greenhorn

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posted 11 years ago

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Hello this is my first message. I'm learning Java and studying the collection framework. I've found an exercise that is driving me crazy. I'd like to have some advices to solve it.

this is the text:
Write a static method boolean componibile(List <character> l,String s) that, given a list of alphabetic characters (which includes also the wildcard '*') and a string, returns true if the
string can be composed using the characters in the list, and false otherwise. Write the solution in order to compile and run the following test schedule without having to edit it:

Thank you

Jeff Verdegan

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posted 11 years ago

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Hi, and welcome to the Ranch!

You'll find your experience here a lot more productive and rewarding if you take your best shot at solving it yourself, show us what you've done so far, and ask a specific question about the specific bits that are giving you trouble.

And remember: Break the problem up into the smallest pieces you can, and work on solving one piece first before moving on to the next one.

Good luck!

Winston Gutkowski

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posted 11 years ago

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Simone Sarigu wrote:this is the text:

Hi Simone, and welcome to JavaRanch.

I've broken up those very long lines of yours because they screw up the windowing here (it's also bad programming practise).

Please re-read the UseCodeTags (←click) page thoroughly.

Thanks.

Winston

Simone Sarigu

Greenhorn

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posted 11 years ago

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Ok I'm posting the class i've write. It doesn't work and throw a NoSuchElementException.
Hope this won't screw up the page again.

import java.util.*;

public class Scarabeo {
    
    public static boolean componibile(List<Character> l, String s){
       
        char[] c=arrChar(l.iterator(),new char[l.size()]);
        return componibile(c,s);
    }
    
    private static boolean componibile(char[] arr, String s){
        if(s.length()==0)
            return false;
        if(!find(arr,s.charAt(0))){
            
        if(!find(arr,'*')){
        return false;
        }
        else 
            if(s.length()==1)
                return true;
                
            else return componibile(arr,s.substring(1));
        }
        else{
             if(s.length()==1)
             return true;
             else
             return componibile(arr,s.substring(1));
        }
        
    }
    
    private static char[] arrChar(Iterator it, char[] c){
    
        if(it.hasNext()){
            for(int i = 0; i<=c.length;i++){
                c[i]=(Character)(it.next());
                
            }
            return c;
        }
        else 
            return c;
    }
    
    private static boolean find(char[]arr, char ch){
        
        for(int i = 0;i<=arr.length;i++){
            if(arr[i]!='&'&&Character.toUpperCase(arr[i])==Character.toUpperCase(ch)){
                arr[i]='&';
                return true;
            }
            else
            return find(arr,ch);
        }
        return false;
    }
}

Thank you

Jeff Verdegan

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posted 11 years ago

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It will be easier to help you if you copy/paste the exact, complete error message, including at least the first several lines of the stack trace, and indicate clearly which line caused the problem.

fred rosenberger

lowercase baba

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posted 11 years ago

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We are always happy to help...but the details are always CRITICALLY important. "It doesn't work" doesn't really tell us the problem.

Does it compile? Does it run? Does it crash partway through?

I can guess that the latter is the case...but when it throws that exception, it gives you information on where EXACTLY that is happening. Please post the entire error message, not just a paraphrase of it.

I even went as far as trying to compile all your code. The ProvaScarabeo class gives me 6 errors. The Scarabeo compiles, but I can't run it since it doesn't have a main. So I can't help you any further.

There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors

Simone Sarigu

Greenhorn

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posted 11 years ago

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Thank you guys for your patience. In the ProvaScarabeo class was missing an import. I can't edit the first post: import java.util.*;

Exception in thread "main" java.util.NoSuchElementException
at java.util.ArrayList$Itr.next(ArrayList.java:794)
at esercizioundici.Scarabeo.arrChar(Scarabeo.java:38)
at esercizioundici.Scarabeo.componibile(Scarabeo.java:07)
at esercizioundici.ProvaScarabeo.main(ProvaScarabeo.java:24)
Java Result: 1

Campbell Ritchie

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posted 11 years ago

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That Exception suggests you are trying to get something out of the List which was never put into the List in the first place. Please make sure that all 26 letters have been entered into the List.

Jeff Verdegan

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Exactly. You're calling next() when there is no next() element.

Simone Sarigu

Greenhorn

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posted 11 years ago

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Thanks to all. I tried to remove those loops inside the methods and use a counter as parameter and now works.
I can't figure out why the other way didn't work. Hints are appreciated ;)

import java.util.*;

public class Scarabeo {
    
    public static boolean componibile(List<Character> l, String s){
       
        char[] c=arrChar(l.iterator(),0,new char[l.size()]);
        return componibile(c,s);
    }
    
    private static boolean componibile(char[] arr, String s){
        if(s.length()==0)
            return false;
        if(!find(arr,0,s.charAt(0))){
            
        if(!find(arr,0,'*')){
        return false;
        }
        else 
            if(s.length()==1)
                return true;
                
            else return componibile(arr,s.substring(1));
        }
        else{
             if(s.length()==1)
             return true;
             else
             return componibile(arr,s.substring(1));
        }
        
    }
    
    private static char[] arrChar(Iterator it, int count, char[] c){
    
        if(it.hasNext()){
            c[count]=(Character)(it.next());
            return arrChar(it,++count,c);
        }
        else 
            return c;
    }
    
    private static boolean find(char[]arr,int count, char ch){
       
       if(count==arr.length)
            return false;
        else{
            if(arr[count]!='&'&&Character.toUpperCase(arr[count])
               ==Character.toUpperCase(ch)){
            arr[count]='&';
            return true;
            }
	else
	return find(arr,++count,ch);
	}
      
    }
}

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