Java Method for removing duplicates from char array

Question

I have a char array filled by the user ( arrayInput[] ) with some characters, like {b, d, a, b, f, a, g, a, a, f}, and I need to create a method which returns a new char array with only the first occurrence of the character, but in the order of input. The book also says "A way to solve this problem is to create a boolean array to keep track of the characters to mantain!", but I can't imagine how the boolean array should work with the other arrays.

The main problem is that I can save in a boolean array if arrayInput contains a specific character, and even how many times, but only creating a very long ramified if-else into a for, like

    if ((arrayOutput[i] == 'A') && (arrayControl[0] = false)) {
        arrayControl[0] = true;  }

where arrayOutput is the array I want to return from the method, arrayControl[0] is the value of 'A' in my boolean array I created into the method. A = 0, B = 1, ... Z = 25, a = 26, b = 27, ... 51 = z. For every single character, uppercase and lowercase, I created a place into the array, so I could check everything, but now I can't go any further. I don't know how to save the characters on arrayOutput , how to check if a character is already on arrayOutput and if it's already there, the array passes that specific character and go to the next one.

Also please remember I'm a newbie, so I know very little about Java. Please explain yourself the best you can. Thanks in advance!

Answer 1

This could work:

public static void main(String[] args) {
    Main main = new Main();
    char[] array = {'e','a','b','a','c','d','b','d','c','e'};
    main.getCharArray(array);
}

private char[] getCharArray(char[] array) {
    String _array = "";
    for(int i = 0; i < array.length; i++) {
        if(_array.indexOf(array[i]) == -1) // check if a char already exist, if not exist then return -1
            _array = _array+array[i];      // add new char
    }
    return _array.toCharArray();
}

Output:

eabcd

Answer 2

 boolean arr[26]; //considering only small letters arrive. otherwise take a larger array.
for( i=0;i<str.length;i++ )
  arr[str[i]-'a']=true;

The ones at last after the loop are true are the actual character. (all duplicates eleminated).

To take into consideration the positions,

int arr[26];
  //initialize all the array elemnts to 0
  for( i=0;i<str.length();i++ )
      if(i>=arr[str[i]-'a'])
            arr[str[i]-'a']=i+1;

//Those greater than 0 are non-duplicated characters. Their poistion of first occurence= (arr[i]-1)

EDIT: I have last used java almost a year ago. The algorithm is shown properly. Sorry for my awkward java code.

Answer 3

This might help. Make a separate array and store only non-duplicate characters.

char[] removeDuplicates (char[] arrayInput) {
    boolean exists[]=new boolean[26];
    char arrayOutput[] = new char[26];
    int ctr=0;
    for(int i=0; i<26; i++) {
        exists[i] = false;
    }
    for(int i=0; i<arrayInput.length; i++) {
        if(!exists[arrayInput[i]-97]) {
            exists[arrayInput[i]-97]=true;
            arrayOutput[ctr++]=arrayInput[i];
        }
    }

   return Arrays.copyOfRange(arrayOutput, 0, ctr);

}

Answer 4

If you consider using of collection framework then it would be much easier. Your array of char with duplicate is arrayInput . Now put each char from it to a HashSet like this -

HashSet<Character> uniqueCharSet = new HashSet<Character>();
for(char each : arrayInput){

   uniqueCharSet.add(each);
}   

Now the HashSet uniqueCharSet will contains only the unique characters from the char array arrayInput . Note here all element in uniqueCharSet are wrapper type - Character .

You can convert the HashSet uniqueCharSet to array of Character like this -

Object[] uniqueCharArray = uniqueCharSet.toArray();

And then you can use them like this -

for(Object each : uniqueCharArray){
   Character c = (Character) each;
   System.out.println(c);
}

Answer 5

Here's the method to achieve what you need:

public static void main(String[] args) {
    char[] arr= {'A','B','C','A','B'};

    HashSet<Character> hset=new HashSet<Character>();

    for(int i=0;i<arr.length;i++) {
        hset.add(arr[i]);
        }

    Object[] ObjChar=hset.toArray();

    char[] resultArr = new char[ObjChar.length];

    for(int j=0;j<ObjChar.length;j++) {

    resultArr[j]=(char) ObjChar[j];
    }

    for(char eachChar: resultArr) {

        System.out.println(eachChar);
    }
}