How to Calculate String Rotation in Java

The challenge

Write a function that receives two strings and returns n, where n is equal to the number of characters we should shift the first string forward to match the second. The check should be case-sensitive.

For instance, take the strings “fatigue” and “tiguefa”. In this case, the first string has been rotated 5 characters forward to produce the second string, so 5 would be returned. If the second string isn’t a valid rotation of the first string, the method returns -1.

Examples:

"coffee", "eecoff" => 2
"eecoff", "coffee" => 4
"moose", "Moose" => -1
"isn't", "'tisn" => 2
"Esham", "Esham" => 0
"dog", "god" => -1

The solution in Java code

Option 1:

public class CalculateRotation {
  static int shiftedDiff(String first, String second){
    if (first.length() != second.length()) return -1;
    return (second + second).indexOf(first);
  }
}

Option 2:

public class CalculateRotation {
  static int shiftedDiff(String first, String second) {
    return (first.length() <= second.length()) ?
           (second + second).indexOf(first) : -1;
  }
}

Option 3:

public class CalculateRotation {
   static int shiftedDiff(String first, String second){
        for (int i = 0; i <= first.length(); i++) {
            if (second.equals(first)) return i;
            first = shift(first);
        }
        return -1;
    }

    private static String shift(String word) {
        return word.substring(word.length() - 1) + word.substring(0, word.length() - 1);
    }
}

Test cases to validate our solution

import org.junit.Test;
import static org.junit.Assert.assertEquals;
import org.junit.runners.JUnit4;

public class RotationTest {
    @Test
    public void test() {
      assertEquals(-1, CalculateRotation.shiftedDiff("hoop","pooh"));
      assertEquals(2, CalculateRotation.shiftedDiff("coffee","eecoff"));
      assertEquals(4, CalculateRotation.shiftedDiff("eecoff","coffee"));
    }
}