codewars070 - Simple Encryption #1 - Alternating Split

Instructions

https://www.codewars.com/kata/simple-encryption-number-1-alternating-split/train/java

Solution:

public class Kata {


	private static String alternatingSplit(final String text) {
		StringBuilder sb = new StringBuilder();
		final int len = text.length();
		final int step = len / 2;
		int pos = 1;
		for (int i = 0; i < step; i++) {
			sb.append(text.charAt(pos));
			pos += 2;
		}
		pos = 0;
		for (int i = 0; i < step; i++) {
			sb.append(text.charAt(pos));
			pos += 2;
		}
		if (len % 2 == 1) {
			sb.append(text.charAt(len - 1));
		}

		return sb.toString();
	}

	public static String encrypt(final String text, final int n) {
		if (text == null || "".equals(text.trim()) || n <= 0
				|| text.length() == 1) {
			return text;
		}
		String result = text;
		for (int i = 0; i < n; i++) {
			result = alternatingSplit(result);
		}
		return result;
	}

	private static String restore(final String encryptedText) {
		StringBuilder sb = new StringBuilder();
		final int len = encryptedText.length();
		final int step = len / 2;
		for (int i = 0; i < step; i++) {
			sb.append(encryptedText.charAt(step + i));
			sb.append(encryptedText.charAt(i));
		}
		if (len % 2 == 1) {
			sb.append(encryptedText.charAt(len - 1));
		}

		return sb.toString();
	}

	public static String decrypt(final String encryptedText, final int n) {
		if (encryptedText == null || "".equals(encryptedText.trim()) || n <= 0
				|| encryptedText.length() == 1) {
			return encryptedText;
		}
		String result = encryptedText;
		for (int i = 0; i < n; i++) {
			result = restore(result);
		}
		return result;
	}


  
}

Sample Tests:

import org.junit.Test;
import static org.junit.Assert.*;

public class ExampleTests {

  @Test
  public void testEncrypt() {
    // assertEquals("expected", "actual");
    assertEquals("This is a test!", Kata.encrypt("This is a test!", 0));
    assertEquals("hsi  etTi sats!", Kata.encrypt("This is a test!", 1));
    assertEquals("s eT ashi tist!", Kata.encrypt("This is a test!", 2));
    assertEquals(" Tah itse sits!", Kata.encrypt("This is a test!", 3));
    assertEquals("This is a test!", Kata.encrypt("This is a test!", 4));
    assertEquals("This is a test!", Kata.encrypt("This is a test!", -1));
    assertEquals("hskt svr neetn!Ti aai eyitrsig", Kata.encrypt("This kata is very interesting!", 1));
  }
    
  @Test
  public void testDecrypt() {
    // assertEquals("expected", "actual");
    assertEquals("This is a test!", Kata.decrypt("This is a test!", 0));
    assertEquals("This is a test!", Kata.decrypt("hsi  etTi sats!", 1));
    assertEquals("This is a test!", Kata.decrypt("s eT ashi tist!", 2));
    assertEquals("This is a test!", Kata.decrypt(" Tah itse sits!", 3));
    assertEquals("This is a test!", Kata.decrypt("This is a test!", 4));
    assertEquals("This is a test!", Kata.decrypt("This is a test!", -1));
    assertEquals("This kata is very interesting!", Kata.decrypt("hskt svr neetn!Ti aai eyitrsig", 1));
  }
    
  @Test
  public void testNullOrEmpty() {
    // assertEquals("expected", "actual");
    assertEquals("", Kata.encrypt("", 0));
    assertEquals("", Kata.decrypt("", 0));
    assertEquals(null, Kata.encrypt(null, 0));
    assertEquals(null, Kata.decrypt(null, 0));
  }

}