Java-Programming/AufgabenBlatt4/src/Aufgabe7.java

import org.junit.Test;

import static junit.framework.TestCase.assertFalse;
import static junit.framework.TestCase.assertTrue;

/**
 * Generic test class for implementing and testing palindrome detection
 *                _ _   _               _
 * __      ___ __(_) |_| |_ ___ _ __   | |__  _   _
 * \ \ /\ / / '__| | __| __/ _ \ '_ \  | '_ \| | | |
 *  \ V  V /| |  | | |_| ||  __/ | | | | |_) | |_| |
 *   \_/\_/ |_|  |_|\__|\__\___|_| |_| |_.__/ \__, |
 *                                            |___/
 *  ____                  __     __               _
 * / ___|_   _____ _ __   \ \   / /__   __ _  ___| |
 * \___ \ \ / / _ \ '_ \   \ \ / / _ \ / _` |/ _ \ |
 *  ___) \ V /  __/ | | |   \ V / (_) | (_| |  __/ |
 * |____/ \_/ \___|_| |_|    \_/ \___/ \__, |\___|_|
 *                                     |___/
 * Licensed under the GPLv2 License, Version 2.0 (the "License");
 * Copyright (c) Sven Vogel
 */
public class Aufgabe7 {

    /**
     * Tests whether the supplied string is a palindrome or not using iterations
     *
     * @implNote returns true if the supplied string is smaller than 2 or blank
     * @param text the string to test
     * @return true if the supplied string is a palindrome, false otherwise
     */
    private static boolean isPalindrome(String text) {
        if (text.isBlank() || text.length() < 2)
            return true;

        for (int i = 0; i < text.length() / 2; i++) {
            if (text.charAt(i) != text.charAt(text.length() - i - 1))
                return false;
        }

        return true;
    }

    /**
     * Tests whether the supplied string is a palindrome or not using recursion
     *
     * @implNote returns true if the supplied string is smaller than 2 or blank
     * @param text the string to test
     * @return true if the supplied string is a palindrome, false otherwise
     */
    private static boolean isPalindromeRecursive(String text) {
        if (text.isBlank() || text.length() < 2)
            return true;

        if (text.charAt(0) != text.charAt(text.length() - 1))
            return false;

        return isPalindromeRecursive(text.substring(1, text.length() - 1));
    }

    /**
     * Tests whether the supplied string is a palindrome or not by iteration
     * also ignores case
     *
     * @implNote returns true if the supplied string is smaller than 2 or blank
     * @param text the string to test
     * @return true if the supplied string is a palindrome, false otherwise
     */
    private static boolean isPalindromeIgnoreCase(String text) {
        if (text.isBlank() || text.length() < 2)
            return true;

        var lowerCase = text.toLowerCase();

        for (int i = 0; i < text.length() / 2; i++) {
            if (lowerCase.charAt(i) != lowerCase.charAt(text.length() - i - 1))
                return false;
        }

        return true;
    }

    /**
     * Test iterative palindrome detection
     */
    @Test
    public void testLowercaseIterative() {
        var PALINDROMES = new String[]{
                "otto",
                "121",
                "regallager",
                "reliefpfeiler"
        };

        // palindromes
        for (var palindrome : PALINDROMES) {
            assertTrue(isPalindrome(palindrome));
        }

        var NO_PALINDROMES = new String[]{
                "abcdefghijklmnopqrstuvwxyz",
                "sven vogel",
                "koeffizient"
        };

        // no palindromes
        for (var noPalindrome : NO_PALINDROMES) {
            assertFalse(isPalindrome(noPalindrome));
        }
    }

    /**
     * Test recursive palindrome detection
     */
    @Test
    public void testLowercaseRecursive() {
        var PALINDROMES = new String[]{
                "otto",
                "121",
                "regallager",
                "reliefpfeiler"
        };

        // palindromes
        for (var palindrome : PALINDROMES) {
            assertTrue(isPalindromeRecursive(palindrome));
        }

        var NO_PALINDROMES = new String[]{
                "abcdefghijklmnopqrstuvwxyz",
                "sven vogel",
                "koeffizient"
        };

        // no palindromes
        for (var noPalindrome : NO_PALINDROMES) {
            assertFalse(isPalindromeRecursive(noPalindrome));
        }
    }

    /**
     * Test iterative palindrome detection with ignore case
     */
    @Test
    public void testIgnoreCaseIterative() {
        var PALINDROMES = new String[]{
                "OtTo",
                "121",
                "ReGaLlAgeR",
                "reLiEfPfeIler"
        };

        // palindromes
        for (var palindrome : PALINDROMES) {
            assertTrue(isPalindromeIgnoreCase(palindrome));
        }

        var NO_PALINDROMES = new String[]{
                "AbcdeFghijKlmnOpqRstUvwxyz",
                "sVeN vOgeL",
                "kOefFiZiEnt"
        };

        // no palindromes
        for (var noPalindrome : NO_PALINDROMES) {
            assertFalse(isPalindromeIgnoreCase(noPalindrome));
        }
    }
}