import java.util.ArrayList;
import java.util.List;
import java.util.Random;

import edu.emory.mathcs.backport.java.util.Arrays;
import edu.emory.mathcs.backport.java.util.Collections;

public class Test {
	List<String> values = null;
	Random random = new Random();

	public static void main(String[] args) throws Exception {
		new Test().getAllCombinations("abcdefghijrwqtwerqwerwqerwqertwqreqwer", 2).forEach((x) -> {
			System.out.println(x);
		});
	}

	/**
	 * The method finds all combinations of the words in a predetermined range.
	 *
	 * @param text
	 * @param size
	 * @return List<String>
	 */
	public List<String> getAllCombinations(String text, int size) {
		if (text.length() > size) {
			int maxCombination = fact(size);
			values = new ArrayList<>(maxCombination);
			String cutsText = text.substring(0, size);

			List<String> letters = Arrays.asList(cutsText.split(""));
			for (int i = 0; i < maxCombination; i++) {
				getRandomWord(letters);
			}
		} else {
			System.out.println("size is not correct");
		}
		return values;
	}

	private String getRandomWord(List<String> letters) {
		String randomWord = "";

		do {
			randomWord = "";
			Collections.shuffle(letters);
			for (String letter : letters) {
				randomWord = randomWord.concat(letter);
			}
			;
			if (!values.contains(randomWord))
				break;
		} while (true);
		values.add(randomWord);

		return randomWord;
	}

	public int fact(int num) {
		return (num == 0) ? 1 : num * fact(num - 1);
	}

}