finding duplicate characters in a String

[Ravi Kiran Va]

Hi ,

I have this String "Mumbai"

Please tell me how can i parse through the contents of this String and find the
duplicate character ??

[Campbell Ritchie]

Pnecil, paper and eraser. Write down how you intend to do it, then later convert it to code.

[Campbell Ritchie]

Ravi Kiran Va wrote: . . . I have this String "Mumbai" . . . find the duplicate character ??

What duplicate character?

[Ravi Kiran Va]

please tell me how to find duplicate characters in a String??(It can be any character)

[fred rosenberger]

First, you have to define the problem better. Does 'M' equal 'm'? Some people would say yes, others would say no. Until you define the conditions, there is no point in answering.

Next...please read Campbell's first post. Before you write any code, you should have a good idea how you'd do it using nothing more than paper, pencil, and your brain. Don't even consider writing a single line of code until you can write down in a natural language (English, German, Hindi, Esperanto...) how to do it.

Once you have that, writing the java code (or C, or Perl, or assembly) is almost trivial, assuming your algorithm above is well defined.

So, work on that, and when you have something, post it here, and we'll work on the next steps.

[Ravi Kiran Va]

I am searching the net for this , didn't find anything related so the reason i posted

Exmple in the below case , there are two a's repeated .
But i dont want to use it staticlly as str.charAt(i)=='a' .

I want to know dynamically which character is repeating and how many number of times

public class One {
	

	public static void main(String args[])
	{
	
		String str = "java";
		for(int i=0;i<str.length();i++)
		{
		
		}
	}
}

[Henry Wong]

I'll add to the chorus to agree with Campbell. Do it on paper first. After all, if you can't do it on paper, how do you expect to teach the computer how to do it?

Henry

[fred rosenberger]

In case it isn't obvious already, nobody here is going to simply hand you the answer. we're here to help you, not do it for you.

Again, forget about writing a single line of java code. If you didn't have access to a computer, how would YOU find duplicate characters?

[Campbell Ritchie]

fred rosenberger wrote: . . . Campbell's first post. . . . paper, pencil, and your brain. . . .

Good grief! Somebody has used "Campbell" and "brain" on the same line.

Joking aside, Ravi Kiran Va, you are mistaken even to write a class name until you know what you plan to do with it. You didn't say you wanted to know how many repeats there are. Go through the Java™ Tutorials section on Collections, and there is an example which does something surprisingly similar to what you want in there somewhere.

[upanshu vaid]

Hi ,
I accidently hit with this thread and as i have a similar program so I am posting the below code it will help you

public class Same_Occurence_String {
    public static void main(String[] args) {
        String g="heLlo";
      int  count=0;
   for(int i=g.length()-1;i>=0;i--){
   if(g.charAt(i)=='l'|g.charAt(i)=='L' ){
       System.out.println("indexes where duplicate character are"+i);
       count=++count;  
   }
   }
        System.out.println("no. of duplicate character"+count);
    }
}

Thanks

[Jesper de Jong]

Thanks, upanshu vaid.

There are a few minor issues with your code.

First of all, it doesn't really work. The only thing that your code does is find which characters in the string are 'l' or 'L'. Suppose you didn't know beforehand which characters were duplicates - this code would not find them. For example, if I change line 3 to this:

String g = "Mumbai";

then your code would not find the two m's.

Second, you should use the logical OR operator || instead of the bitwise OR operator | in line 6.

Third, line 8 works, but this is not how you should increment the counter: count=++count;

Just write this instead: count++;

[upanshu vaid]

Thanks Jesper de Jong
for your value able points , the code that I wrote was just to show the duplicate character can be find in string , I use static string , now I think I should write that a program that will take string from user and then find the duplicates.
Thanks

[upanshu vaid]

here is the general code to find how many times the single duplicated appear in the string

import java.util.Scanner;

public class Same_Occurence_String {
    public static void main(String[] args) {
        Scanner scan=new Scanner(System.in);
        System.out.println("enter the string");
     String g=   scan.next();
    System.out.println("enter the character you want to search for");
  String l=  scan.next();
 char[] c= l.toCharArray();
   int  count=0;
   for(int i=0;i<=g.length()-1;i++){
       for(int k=0;k<=c.length-1;k++)
       {
   if(g.charAt(i)==c[k]){
       System.out.println("indexes where duplicate character are"+i);
       count++;  
   }
   }
        }
   System.out.println("no. of duplicate character"+count);  
}
}

Thanks

[Gubendran Lakshmanan]

You can use google Guava collections "Multiset". Below is the code.

import com.google.common.collect.Multiset;
import com.google.common.collect.HashMultiset;

public class JavaRanch {
	public static void main(String args[]) {
		 String test = "Mumbai";
			 Multiset<Character> duplicateCount = HashMultiset.create();
			 for (int i=0; i < test.length(); i++) {
				 duplicateCount.add(test.toLowerCase().charAt(i));
			 }
			 for (Character ch : duplicateCount.elementSet()) {
			     System.out.println("Count " + ch + " " + duplicateCount.count(ch));
		         }
		}
}

[Campbell Ritchie]

Welcome to the Ranch

[li stayhere]

Campbell Ritchie wrote:Welcome to the Ranch

That's too complex. Here is an example in Java, I've tested it. I hope it can be help to you.

public static void main(String[] args){
        String s="Don't love me!";

	    s=s.toLowerCase();

	    char[] chAry=s.toCharArray();

	    int[] counter=new int[26];

	    for(char ch:chAry){
	        int idx=ch-'a';
	        if(idx<0 || idx>25){
	           continue;
	        }

	        counter[idx]++;
	    }

	   for(int i=0;i<counter.length;i++){
	        
	        if(counter[i]>1){
	            char ch=(char)('a'+i);
	            System.out.printf("%c is duplicate,duplicate count=%d \r\n", ch,counter[i]);
	        }
	   }
}

[Campbell Ritchie]

Welcome to the Ranch

I can see some complex features in your code, too. Changing to lower case and then subtracting to give numbers between 0 and 25 looks complex to me. Also using continue when a simple if is all you need.

[Winston Gutkowski]

li stayhere wrote:That's too complex...

And you're re-inventing the wheel. Why not use classes that are already written to help you out?:

public static void main(String[] args){
   String s = "Don't love me!";

   s = s.toLowerCase(); // optional

   LinkedHashMap<Character, AtomicInteger> charCounts =
      new LinkedHashMap<Character, AtomicInteger>(s.length());

   for (char ch: s.toCharArray()) {
      AtomicInteger count = charCounts.get(ch);
      if (count == null) // 'ch' wasn't found
         charCounts.put(ch, new AtomicInteger(1));
      else
         count.incrementAndGet();
   }

   for (Map.Entry e : charCounts.entrySet()) {
      int count = e.getValue().get();
      if (count > 1)
         System.out.printf("%c is duplicate, duplicate count=%d %n",
            e.getKey().charValue(), count);
   }
}

I should add that it's only one way of doing it; there are many others.

Winston