Remove duplicate characters in a string in Java

Question

I started to read the famous "cracking the Coding Interview" book.

Design an algorithm and write code to remove the duplicate characters in a string without using any additional buffer. NOTE: One or two additional variables are fine. An extra copy of the array is not.

I found a similar topic here : Remove the duplicate characters in a string

The solution given by the author was that :

  public static void removeDuplicates(char[] str) {
  if (str == null) return;
  int len = str.length;
  if (len < 2) return;

  int tail = 1;

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

       for (j = 0; j < tail; ++j) {
       if (str[i] == str[j]) break;
       }

       if (j == tail) {
       str[tail] = str[i];
       ++tail;
     }
  }
  str[tail] = 0;
 }

The problem here is that the author used an array to be an argument for this function. So my question is : how can you write an algorithms with a STRING as an argument? Because I felt like it's really easier to use an array here and it's like that you "avoid the difficulty" of the exercice (in my opinion, I'm a newly Java developer).

How can you write such an algorithm?

For question's sake, let's assume strings were mutable, say you could remove characters from them: You can use String.charAt(position) to get the character on that position the same as you use array[position]. — Vucko
– Vucko, Commented Apr 24, 2016 at 23:39

Cyb3rFly3r · Accepted Answer · 2016-04-24 23:20:31Z

3

Java strings are immutable, so you can't do it with a string without copying the array into a buffer.

answered Apr 24, 2016 at 23:20

Cyb3rFly3r

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1 Comment

Em Ae Over a year ago

Adding to this ... str[tail] = str[i] is the statement which require an array.

Jack Ammo · Accepted Answer · 2016-04-25 04:57:17Z

for this to work with a String you'd have to return a String from the method that represents the modified str with no duplicates. not sure if it'll go against the rules, but here's how I'd solve the problem with String's:

for each character in the string, i would split the string at that character. i would remove all instances of that character from the latter substring. i would then concatenate the former substring with the modified latter substring, making sure that the character is still kept in it's place. something like this:

public static String removeDuplicates( String str ) {
    if( str == null || str.length() < 2 )
        return str;
    String temp;
    for( int x = 0; x + 1 < str.length(); x++ ) {
        temp = str.charAt( x ) + ""; 
        str = str.substring( 0, x ) + temp + str.substring( x + 1 ).replaceAll( temp, "" );
    }
    return str;
}

ISHAN KUMAR GHOSH · Accepted Answer · 2020-10-05 19:38:57Z

0

In Java 8 we can do it like this

private void removeduplicatecharactersfromstring() {
    String myString = "aabcd eeffff ghjkjkl";
    StringBuilder builder = new StringBuilder();
    System.out.println(myString);
    Arrays.asList(myString.split(" "))
            .forEach(s -> {
                builder.append(Stream.of(s.split(""))
                        .distinct().collect(Collectors.joining()).concat(" "));
            });
    System.out.println(builder); // abcd ef ghjkl
}

answered Oct 5, 2020 at 19:38

ISHAN KUMAR GHOSH

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