refactor: ReturnSubsequence (#5408)

* refactor: ReturnSubsequence

* checkstyle: fix formatting

* checkstyle: fix formatting

---------

Co-authored-by: alxkm <alx@alx.com>

src/test/java/com/thealgorithms/others/ReturnSubsequenceTest.java

@@ -0,0 +1,23 @@
+package com.thealgorithms.others;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+
+import java.util.stream.Stream;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+class ReturnSubsequenceTest {
+
+    @ParameterizedTest
+    @MethodSource("provideTestCases")
+    void testSubsequences(String input, String[] expected) {
+        String[] actual = ReturnSubsequence.getSubsequences(input);
+        assertArrayEquals(expected, actual);
+    }
+
+    static Stream<Arguments> provideTestCases() {
+        return Stream.of(Arguments.of("", new String[] {""}), Arguments.of("a", new String[] {"", "a"}), Arguments.of("ab", new String[] {"", "b", "a", "ab"}), Arguments.of("abc", new String[] {"", "c", "b", "bc", "a", "ac", "ab", "abc"}),
+            Arguments.of("aab", new String[] {"", "b", "a", "ab", "a", "ab", "aa", "aab"}));
+    }
+}