Check if two strings are rotations of each other [BAEL-7493] (#15864)

* feat: string rotation

* fix: test names

algorithms-modules/algorithms-miscellaneous-7/src/main/java/com/baeldung/algorithms/stringrotation/StringRotation.java

@@ -0,0 +1,123 @@
+package com.baeldung.algorithms.stringrotation;
+
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Queue;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+
+public class StringRotation {
+
+    public static boolean doubledOriginContainsRotation(String origin, String rotation) {
+        if (origin.length() == rotation.length()) {
+            return origin.concat(origin)
+              .contains(rotation);
+        }
+
+        return false;
+    }
+
+    public static boolean isRotationUsingCommonStartWithOrigin(String origin, String rotation) {
+
+        if (origin.length() == rotation.length()) {
+
+            List<Integer> indexes = IntStream.range(0, origin.length())
+              .filter(i -> rotation.charAt(i) == origin.charAt(0))
+              .boxed()
+              .collect(Collectors.toList());
+
+            for (int startingAt : indexes) {
+                if (isRotation(startingAt, rotation, origin)) {
+                    return true;
+                }
+            }
+        }
+
+        return false;
+    }
+
+    static boolean isRotation(int startingAt, String rotation, String origin) {
+
+        for (int i = 0; i < origin.length(); i++) {
+            if (rotation.charAt((startingAt + i) % origin.length()) != origin.charAt(i)) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    public static boolean isRotationUsingQueue(String origin, String rotation) {
+
+        if (origin.length() == rotation.length()) {
+            return checkWithQueue(origin, rotation);
+        }
+
+        return false;
+    }
+
+    static boolean checkWithQueue(String origin, String rotation) {
+
+        if (origin.length() == rotation.length()) {
+
+            Queue<Character> originQueue = getCharactersQueue(origin);
+
+            Queue<Character> rotationQueue = getCharactersQueue(rotation);
+
+            int k = rotation.length();
+            while (k > 0 && null != rotationQueue.peek()) {
+                k--;
+                char ch = rotationQueue.peek();
+                rotationQueue.remove();
+                rotationQueue.add(ch);
+                if (rotationQueue.equals(originQueue)) {
+                    return true;
+                }
+            }
+        }
+
+        return false;
+    }
+
+    static Queue<Character> getCharactersQueue(String origin) {
+        return origin.chars()
+          .mapToObj(c -> (char) c)
+          .collect(Collectors.toCollection(LinkedList::new));
+    }
+
+    public static boolean isRotationUsingSuffixAndPrefix(String origin, String rotation) {
+
+        if (origin.length() == rotation.length()) {
+            return checkPrefixAndSuffix(origin, rotation);
+        }
+
+        return false;
+    }
+
+    static boolean checkPrefixAndSuffix(String origin, String rotation) {
+        if (origin.length() == rotation.length()) {
+
+            for (int i = 0; i < origin.length(); i++) {
+                if (origin.charAt(i) == rotation.charAt(0)) {
+                    if (checkRotationPrefixWithOriginSuffix(origin, rotation, i)) {
+                        if (checkOriginPrefixWithRotationSuffix(origin, rotation, i))
+                            return true;
+                    }
+                }
+            }
+
+        }
+
+        return false;
+    }
+
+    private static boolean checkRotationPrefixWithOriginSuffix(String origin, String rotation, int i) {
+        return origin.substring(i)
+          .equals(rotation.substring(0, origin.length() - i));
+    }
+
+    private static boolean checkOriginPrefixWithRotationSuffix(String origin, String rotation, int i) {
+        return origin.substring(0, i)
+          .equals(rotation.substring(origin.length() - i));
+    }
+}

algorithms-modules/algorithms-miscellaneous-7/src/test/java/com/baeldung/algorithms/stringrotation/StringRotationUnitTest.java

@@ -0,0 +1,61 @@
+package com.baeldung.algorithms.stringrotation;
+
+import static com.baeldung.algorithms.stringrotation.StringRotation.doubledOriginContainsRotation;
+import static com.baeldung.algorithms.stringrotation.StringRotation.isRotationUsingCommonStartWithOrigin;
+import static com.baeldung.algorithms.stringrotation.StringRotation.isRotationUsingQueue;
+import static com.baeldung.algorithms.stringrotation.StringRotation.isRotationUsingSuffixAndPrefix;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+
+class StringRotationUnitTest {
+
+    @Test
+    void givenOriginAndRotationInput_whenCheckIfOriginContainsRotation_thenIsRotation() {
+        assertTrue(doubledOriginContainsRotation("abcd", "cdab"));
+        assertTrue(doubledOriginContainsRotation("abcd", "abcd"));
+    }
+
+    @Test
+    void givenOriginAndRotationInput_whenCheckIfOriginContainsRotation_thenNoRotation() {
+        assertFalse(doubledOriginContainsRotation("abcd", "bbbb"));
+        assertFalse(doubledOriginContainsRotation("abcd", "abcde"));
+    }
+
+    @Test
+    void givenOriginAndRotationInput_whenCheckingCommonStartWithOrigin_thenIsRotation() {
+        assertTrue(isRotationUsingCommonStartWithOrigin("abcd", "cdab"));
+        assertTrue(isRotationUsingCommonStartWithOrigin("abcd", "abcd"));
+    }
+
+    @Test
+    void givenOriginAndRotationInput_whenCheckingCommonStartWithOrigin_thenNoRotation() {
+        assertFalse(isRotationUsingCommonStartWithOrigin("abcd", "bbbb"));
+        assertFalse(isRotationUsingCommonStartWithOrigin("abcd", "abcde"));
+    }
+
+    @Test
+    void givenOriginAndRotationInput_whenCheckingUsingQueues_thenIsRotation() {
+        assertTrue(isRotationUsingQueue("abcd", "cdab"));
+        assertTrue(isRotationUsingQueue("abcd", "abcd"));
+    }
+
+    @Test
+    void givenOriginAndRotationInput_whenCheckingUsingQueues_thenNoRotation() {
+        assertFalse(isRotationUsingQueue("abcd", "bbbb"));
+        assertFalse(isRotationUsingQueue("abcd", "abcde"));
+    }
+
+    @Test
+    void givenOriginAndRotationInput_whenCheckingUsingSuffixAndPrefix_thenIsRotation() {
+        assertTrue(isRotationUsingSuffixAndPrefix("abcd", "cdab"));
+        assertTrue(isRotationUsingSuffixAndPrefix("abcd", "abcd"));
+    }
+
+    @Test
+    void givenOriginAndRotationInput_whenCheckingUsingSuffixAndPrefix_thenNoRotation() {
+        assertFalse(isRotationUsingSuffixAndPrefix("abcd", "bbbb"));
+        assertFalse(isRotationUsingSuffixAndPrefix("abcd", "abcde"));
+    }
+}