CharacterRemover.java

package com.example;

import java.util.ArrayList;

/**
 * Created by gokhan on 02/03/17.
 */

public class CharacterRemover {


    public String removeExtraCharacters(String input, int limit) {

        if (input == null)
            return null;

        //throw exception
        if (limit < 0)
            return input;


        //find distinct characters
        ArrayList<Character> mDistinctChars = findDistinctChars(input);
        //throw exception
        if (mDistinctChars == null)
            return input;


        //iterate characters and remove if need
        for (Character character : mDistinctChars) {

            //ignore white  space
            if (Character.isWhitespace(character))
                continue;

            int count = findCharacterCount(character, input);

            if (findCharacterCount(character, input) < limit)
                continue;

            input = removeCharacters(input, character);
        }

        return input;
    }

    /**
     * @param word
     * @return distinct characters
     */
    private ArrayList<Character> findDistinctChars(String word) {

        ArrayList<Character> mDistinctChars = new ArrayList<>();

        char characters[] = word.toCharArray();
        for (Character c : characters) {

            if (!mDistinctChars.contains(c))
                mDistinctChars.add(c);
        }

        return mDistinctChars;
    }

    /***
     * @param word
     * @param c
     * @return remove wanted character
     */
    private String removeCharacters(String word, char c) {

        return word.replaceAll(String.valueOf(c), "");
    }

    /**
     * @param word
     * @param c
     * @return remove wanted word
     */
    private String removeCharacters(String word, String c) {

        return word.replaceAll(c, "");
    }


    /**
     * @param c    search character
     * @param word
     * @return count of character
     */
    private int findCharacterCount(char c, String word) {

        if (word == null || word.length() == 0)
            return 0;

        char wordChars[] = word.toCharArray();
        int counter = 0;

        for (int index = 0; index < wordChars.length; index++) {

            if (wordChars[index] == c)
                counter++;
        }

        return counter;
    }
}