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Thread: any idea?StringBuilder

  1. #1
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    Default any idea?StringBuilder

    Hello everyone,
    how can i replace each letter for example "abcde" to "edcba" with StringBuilder only and without the reverse tool
    this is what i tried:
    StringBuilder str=new StringBuilder("abcde");
    		int indexBegin=0;
    		int indexEnd=4;
     
    		for(int i=0;i<str.length();i++){
    			str.setCharAt(i, str.charAt(indexEnd));
    			indexEnd--;
    		}
     
    		System.out.println(str);
    the output is:edcde with i understand why its wrong ,the last two letters already swap so it didnt take from the original str.
    any thoughts how to improve it?
    thanks:}

  2. #2
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    Default Re: any idea?StringBuilder

    Well, you almost answered your own question. If you do it like this you will overwrite one half of the buffered string before you can use all characters. The simple solution is to make a local copy of the String, a backup you might say, so that you always have full access to all characters at any point in time.

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    Default Re: any idea?StringBuilder

    great i understoond and it works well via for loops.
    what isnt it working with my recursion:
    public  static void switchLetters(StringBuilder str,int indexBegin,int indexEnd){
    		StringBuilder k=new StringBuilder(str);
    		if(indexEnd==0){
    			return;
    		}
     
    		str.setCharAt(indexBegin, k.charAt(indexEnd));
     
    		switchLetters(str,++indexBegin,--indexEnd);
     
    		System.out.println(str);
    	}
    in recursion it return only "edcde" what isnt it work here?

  4. #4
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    Default Re: any idea?StringBuilder

    Try to write both "str" and "k" to System.out in every step of the recursion and have a look if you can figure out your problem on your own.
    If you dont see it, reply again and tell us what you have problems with.

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