diff --git a/core-java/src/main/java/com/baeldung/string/Palindrome.java b/core-java/src/main/java/com/baeldung/string/Palindrome.java new file mode 100644 index 0000000000..03b65d1a84 --- /dev/null +++ b/core-java/src/main/java/com/baeldung/string/Palindrome.java @@ -0,0 +1,53 @@ +package com.baeldung.string; + +public class Palindrome { + + public boolean isPalindrome(String text) { + text = text.replaceAll("\\s+", "") + .toLowerCase(); + int length = text.length(); + int forward = 0; + int backward = length - 1; + boolean palindrome = true; + while (backward > forward) { + char forwardChar = text.charAt(forward++); + char backwardChar = text.charAt(backward--); + if (forwardChar != backwardChar) + return false; + } + return palindrome; + } + + public boolean isPalindromeReverseTheString(String text) { + String reverse = ""; + text = text.replaceAll("\\s+", "").toLowerCase(); + char[] plain = text.toCharArray(); + for (int i = plain.length - 1; i >= 0; i--) + reverse += plain[i]; + return reverse.equals(text); + } + + public boolean isPalindromeUsingStringBuilder(String text) { + StringBuilder plain = new StringBuilder(text); + StringBuilder reverse = plain.reverse(); + return reverse.equals(plain); + } + + public boolean isPalindromeUsingStringBuffer(String text) { + StringBuffer plain = new StringBuffer(text); + StringBuffer reverse = plain.reverse(); + return reverse.equals(plain); + } + + public boolean isPalindromeRecursive(String text, int forward, int backward) { + if (forward == backward) + return true; + if ((text.charAt(forward)) != (text.charAt(backward))) + return false; + if (forward < backward + 1) { + return isPalindromeRecursive(text, forward + 1, backward - 1); + } + + return true; + } +} diff --git a/core-java/src/test/java/com/baeldung/string/WhenCheckingPalindrome.java b/core-java/src/test/java/com/baeldung/string/WhenCheckingPalindrome.java new file mode 100644 index 0000000000..e3655a3140 --- /dev/null +++ b/core-java/src/test/java/com/baeldung/string/WhenCheckingPalindrome.java @@ -0,0 +1,114 @@ +package com.baeldung.string; + +import java.util.Arrays; + +import org.junit.Assert; +import org.junit.Test; + +public class WhenCheckingPalindrome { + + private String[] words = { + "Anna", + "Civic", + "Kayak", + "Level", + "Madam", + }; + + private String[] sentences = { + "Sore was I ere I saw Eros", + "Euston saw I was not Sue", + "Too hot to hoot", + "No mists or frost Simon", + "Stella won no wallets" + }; + + private Palindrome palindrome = new Palindrome(); + + @Test + public void whenWord_shouldBePalindrome() { + for(String word:words) + Assert.assertTrue(palindrome.isPalindrome(word)); + } + + @Test + public void whenSentence_shouldBePalindrome() { + for(String sentence:sentences) + Assert.assertTrue(palindrome.isPalindrome(sentence)); + } + + @Test + public void whenReverseWord_shouldBePalindrome() { + for(String word:words) + Assert.assertTrue(palindrome.isPalindromeReverseTheString(word)); + } + + @Test + public void whenReverseSentence_shouldBePalindrome() { + for(String sentence:sentences) + Assert.assertTrue(palindrome.isPalindromeReverseTheString(sentence)); + } + + @Test + public void whenStringBuilderWord_shouldBePalindrome() { + for(String word:words) + Assert.assertTrue(palindrome.isPalindromeUsingStringBuilder(word)); + } + + @Test + public void whenStringBuilderSentence_shouldBePalindrome() { + for(String sentence:sentences) + Assert.assertTrue(palindrome.isPalindromeUsingStringBuilder(sentence)); + } + + @Test + public void whenStringBufferWord_shouldBePalindrome() { + for(String word:words) + Assert.assertTrue(palindrome.isPalindromeUsingStringBuffer(word)); + } + + @Test + public void whenStringBufferSentence_shouldBePalindrome() { + for(String sentence:sentences) + + Assert.assertTrue(palindrome.isPalindromeUsingStringBuffer(sentence)); + } + + @Test + public void whenPalindromeRecursive_wordShouldBePalindrome() { + for(String word:words) { + word = word.replaceAll("\\s+", "").toLowerCase(); + int backward = word.length()-1; + + Assert.assertTrue(palindrome.isPalindromeRecursive(word,0,backward)); + } + } + + @Test + public void whenPalindromeRecursive_sentenceShouldBePalindrome() { + for(String sentence:sentences) { + sentence = sentence.replaceAll("\\s+", "").toLowerCase(); + int backward = sentence.length()-1; + + Assert.assertTrue(palindrome.isPalindromeRecursive(sentence,0,backward)); + } + } + + @Test + public void whenPalindromeStreams_wordShouldBePalindrome() { + String[] expected = Arrays.stream(words) + .filter(palindrome::isPalindrome) + .toArray(String[]::new); + + Assert.assertArrayEquals(expected, words); + } + + @Test + public void whenPalindromeStreams_sentenceShouldBePalindrome() { + String[] expected = Arrays.stream(sentences) + .filter(palindrome::isPalindrome) + .toArray(String[]::new); + + Assert.assertArrayEquals(expected, sentences); + } +}