How to delete duplicate characters in a string?

Question

I have a method that supposed to delete all the dups from string passed inside it. I can print the dups, how can I delete them in the original string ? Say, 'miami' will need to be 'mia' when it will return. Thanks.

  public static String removeDups( String str1){

        char[] str = str1.toCharArray();
        if (str == null) return null;
        int len = str.length;
        if (len < 2) return new String(str);

        char[] newStr = new char[len+1];  
        int copyLength = 0; 

        for ( int i = 1 ; i < len; i++){

            for( int j=0; j< i; j++){

                if ( str[i] == str[j]){
                    System.out.println(" str[i] == str[j] = "+ str[i] + " , "+str[j]);
                    break; 
                }

            }

        }

        return new String(str); 
    }

Duplicate question http://stackoverflow.com/a/4989150/1638718 — ooozguuur, Jul 13 '15 at 15:13
there's no need to convert to char array, use "charAt" to index a string — Brandon Ling, Jul 13 '15 at 15:13
A quick note - your j loop should start at "I" not 0, e.g. j = I; That way it will no loop over previous characters. — Sh4d0wsPlyr, Jul 13 '15 at 15:14
possible duplicate of [Removing duplicates from a String in Java](http://stackoverflow.com/questions/4989091/removing-duplicates-from-a-string-in-java) — ooozguuur, Jul 13 '15 at 15:14

Shar1er80 · Accepted Answer · 2015-07-13T16:54:02.580

I found this to be easier using a StringBuilder rather than a String

EDIT

This can also be done with a combination of StringBuilder and regex

Regex Pattern breakdown:

 (.)    --> matches any character and puts in group 1. 
 ?=     --> this is called a positive lookahead. 
 ?=.*\\1  --> positive lookahead of zero or more characters for the first group

Code Sample:

public static void main(String[] args) throws Exception {
    System.out.println(removeDuplicates("miamimiamimiami"));
    System.out.println(removeDuplicatesRegex("miamimiamimiami"));
}

public static String removeDuplicates(String input){
    StringBuilder data = new StringBuilder(input);
    for (int i = 0; i < data.length(); i++) {
        String character = String.valueOf(data.charAt(i));
        int dupIndex = data.indexOf(character, i + 1);
        while (dupIndex != -1) {
            data.deleteCharAt(dupIndex);
            dupIndex = data.indexOf(character, i + 1);
        }
    }

    return data.toString();
}

public static String removeDuplicatesRegex(String input) {

    return new StringBuilder(
            new StringBuilder(input)
                    .reverse()
                    .toString()
                    .replaceAll("(.)(?=.*\\1)", ""))
            .reverse().toString();
}

Results:

mia
mia

Thanks a lot, this works. You may have a look in my original question ? — Monica Hübner, Jul 13 '15 at 16:06
@MonicaHübner What do you want me to look at? If my answer solved your question, kindly check the check mark next to my answer. — Shar1er80, Jul 13 '15 at 16:21
Hello, I would like to solve it without StringBuilder. Not the original question, I meant code of the modified question. I can now print all the dups, just need to delete them in the original String. Thanks — Monica Hübner, Jul 13 '15 at 16:32
I really like to answer with reggae. could you please explain how this works, specially replaceAll("(.)(?=.*\\1)", "") part is quite confusing. — Monica Hübner, Jul 13 '15 at 16:42

score 1 · Answer 2 · answered Jul 13 '15 at 16:27

Here's another option:

  StringBuffer buf = new StringBuffer( originalString);
  int len = str.length();
  for (int i = 0; i < len; i++) {
     char c = buf.charAt( i );
     for (int j = len - 1; j > i; j--) {
        if ( buf.charAt( j ) == c ) {
           buf.deleteCharAt( j );
           len--;
        }
     }
  }

score 1 · Answer 3 · answered Jul 13 '15 at 16:32

Remove all duplicate chars in a String:

public static String removeDuplicates(String str1) {

    if (str1 == null)
        return null;

    char[] str = str1.toCharArray();

    int len = str.length;

    if (len < 2)
        return str1;

    char temp = str[0];

    for (int i = 1; i < len; i++) {

        if (temp != 0)
            for (int j = i; j < len; j++)
                if (temp == str[j])
                    str[j] = 0;

        temp = str[i];
    }

    int i = 0;

    char[] str2 = new char[len];

    for (char c : str)
        if (c != 0)
            str2[i++] = c;

    return (new String(str2)).trim();
}

Thanks for your answer. – Monica Hübner Jul 13 '15 at 16:54 — Monica Hübner, Jul 13 '15 at 16:54

Hemant Nigam · Answer 4 · 2015-07-14T07:46:47.570

1

You can also use Arraylist to store the unique characters:

public static String removeDups( String str1){
ArrayList<Character> set=new ArrayList<Character>();
    char[] str=str1.toCharArray();
    for(int i=0;i<str.length;i++)
     {
        if(!set.contains(str[i])){
            set.add(str[i]);
        }
     }
    for(char e:set)
    {
        System.out.print(e);
    }    
}

edited Jul 14 '15 at 07:46

answered Jul 14 '15 at 07:28

Hemant Nigam

31
2

Thanks, need to correct the return statement though. We can return String with StringBuilder StringBuilder builder = new StringBuilder(set.size()); for(char e:set){ builder.append(e); } return builder.toString(); – Monica Hübner Jul 14 '15 at 22:07
Yeah, we can use this to return the String – Hemant Nigam Jul 15 '15 at 17:28

score 0 · Answer 5 · edited May 23 '17 at 10:26

Your loop seems to be a bit strange.

char[] str = str1.toCharArray();
int len = str.length;
if (str == null || len  < 2) return null;

char[] newStr = new char[len+1];  
int newStrLength = 0;  

for( int i = 1; i < len; i++ ){  //Iterate complete string
    for(  int j=0; j < i; j++ ){  //Iterate the already-finished part
        if( str[i] == str[j] ) 
            break; 
        }
        newStr[newStrLength++] = str[i];
    }
}
newStr[newStrLength] = 0;

In this example I make a completly new string and don't alter the original one. It makes the code clearer to read.

Alternatively you could take a look at this question which has some more efficient answers.

Your code is not working (do I need to assume what's copy ? ). I slightly changed the method ( see the question ) and can able to print the dups. How can I delete them in the ORIGINAL string ? Thanks. — Monica Hübner, Jul 13 '15 at 15:51

How to delete duplicate characters in a string?

5 Answers5

EDIT