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string concatenation challenge

Posted on 2014-10-18
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Last Modified: 2014-10-20
Hi,

I am working on below challenge
http://codingbat.com/prob/p117334

I wrote as below
public String stringSplosion(String str) {
  String s="";
  for(int i=0;i<=str.length()-1;i++){
  return (s+str.substring(i));
  
  }
  return null;
}

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My test cases failing as below


Expected      Run            
stringSplosion("Code") → "CCoCodCode"      "Code"      X         
stringSplosion("abc") → "aababc"      "abc"      X         
stringSplosion("ab") → "aab"      "ab"      X         
stringSplosion("x") → "x"      "x"      OK         
stringSplosion("fade") → "ffafadfade"      "fade"      X         
stringSplosion("There") → "TThTheTherThere"      "There"      X         
stringSplosion("Kitten") → "KKiKitKittKitteKitten"      "Kitten"      X         
stringSplosion("Bye") → "BByBye"      "Bye"      X         
stringSplosion("Good") → "GGoGooGood"      "Good"      X         
stringSplosion("Bad") → "BBaBad"      "Bad"      X         

How do i fix and improve my code. Please advise
0
Comment
Question by:gudii9
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7 Comments
 
LVL 20

Assisted Solution

by:n2fc
n2fc earned 668 total points
ID: 40389342
public String stringSplosion(String str) {
  String s="";
  for(int i=0;i<str.length();i++){
     s=s+str.substring(0,i+1);
  }
  return s;
}

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0
 
LVL 16

Accepted Solution

by:
krakatoa earned 664 total points
ID: 40389364
Or
public String stringSplosion(String str) {


StringBuilder sb = new StringBuilder();

for(int y=0;y<str.length()+1;y++){sb.append(str.substring(0,y));}

return sb.toString();

  }

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0
 
LVL 20

Expert Comment

by:n2fc
ID: 40389372
Yet another solution (a tad more arcane):

public String stringSplosion(String str) {
   String s="";
   for(int i=0; i<str.length(); s+=str.substring(0, ++i));
   return s;
}

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0
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LVL 16

Expert Comment

by:krakatoa
ID: 40389386
And one more, slightly better incremental model :

public String stringSplosion(String str) {

StringBuilder sb = new StringBuilder();

for(int y=0;y<str.length();y++){sb.append(str.substring(0,y+1));}

return sb.toString();
  }

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0
 
LVL 7

Author Comment

by:gudii9
ID: 40390039
some reason stringbuilder is not coming to mind.

Let me read these solutions more detail once i get more time
0
 
LVL 16

Expert Comment

by:krakatoa
ID: 40390078
StringBuilder is useful so yes do read the lit on it.
0
 
LVL 32

Assisted Solution

by:awking00
awking00 earned 668 total points
ID: 40392213
gudii9,
You have asked numerous questions involving the manipulation of strings. As I have mentioned in the past a String is an object, not a primitive datatype, and is immutable (meaning it can not be changed). However, methods may be applied to a String (e.g. using charArrays, concatenation, substrings, indexesOf, etc.) to create another String with the desired affect. The StringBuilder class was developed primarily to get around this fact. You seem to have eschewed the use of StringBuilder in favor of other methods, which is fine. It points out that there is almost always more than one way of accomplishing objectives in Java. In certain cases, methods other than StringBuilder might be easier to understand and write but, in many other cases, you will find that StringBuilder offers a better means of manipulating Strings. It behooves you to understand the many tools Java provides such as StringBuilder, which krakatoa suggests, and I second, you read up on.
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