diff --git a/src/main/java/com/thealgorithms/stacks/PalindromeWithStack.java b/src/main/java/com/thealgorithms/stacks/PalindromeWithStack.java new file mode 100644 index 000000000000..98c439341a21 --- /dev/null +++ b/src/main/java/com/thealgorithms/stacks/PalindromeWithStack.java @@ -0,0 +1,57 @@ +package com.thealgorithms.stacks; + +import java.util.LinkedList; + +/** + * A class that implements a palindrome checker using a stack. + * The stack is used to store the characters of the string, + * which we will pop one-by-one to create the string in reverse. + * + * Reference: https://www.geeksforgeeks.org/check-whether-the-given-string-is-palindrome-using-stack/ + */ +public class PalindromeWithStack { + private LinkedList stack; + + /** + * Constructs an empty stack that stores characters. + */ + public PalindromeWithStack() { + stack = new LinkedList(); + } + + /** + * Check if the string is a palindrome or not. + * Convert all characters to lowercase and push them into a stack. + * At the same time, build a string + * Next, pop from the stack and build the reverse string + * Finally, compare these two strings + * + * @param string The string to check if it is palindrome or not. + */ + public boolean checkPalindrome(String string) { + // Create a StringBuilder to build the string from left to right + StringBuilder stringBuilder = new StringBuilder(string.length()); + // Convert all characters to lowercase + String lowercase = string.toLowerCase(); + + // Iterate through the string + for (int i = 0; i < lowercase.length(); ++i) { + char c = lowercase.charAt(i); + // Build the string from L->R + stringBuilder.append(c); + // Push to the stack + stack.push(c); + } + + // The stack contains the reverse order of the string + StringBuilder reverseString = new StringBuilder(stack.size()); + // Until the stack is not empty + while (!stack.isEmpty()) { + // Build the string from R->L + reverseString.append(stack.pop()); + } + + // Finally, compare the L->R string with the R->L string + return reverseString.toString().equals(stringBuilder.toString()); + } +} diff --git a/src/test/java/com/thealgorithms/stacks/PalindromeWithStackTest.java b/src/test/java/com/thealgorithms/stacks/PalindromeWithStackTest.java new file mode 100644 index 000000000000..47b21d5e9e9c --- /dev/null +++ b/src/test/java/com/thealgorithms/stacks/PalindromeWithStackTest.java @@ -0,0 +1,77 @@ +package com.thealgorithms.stacks; + +import static org.junit.jupiter.api.Assertions.assertFalse; +import static org.junit.jupiter.api.Assertions.assertTrue; + +import org.junit.jupiter.api.BeforeEach; +import org.junit.jupiter.api.Test; + +public class PalindromeWithStackTest { + + private PalindromeWithStack palindromeChecker; + + @BeforeEach + public void setUp() { + palindromeChecker = new PalindromeWithStack(); + } + + @Test + public void testValidOne() { + String testString = "Racecar"; + assertTrue(palindromeChecker.checkPalindrome(testString)); + } + + @Test + public void testInvalidOne() { + String testString = "James"; + assertFalse(palindromeChecker.checkPalindrome(testString)); + } + + @Test + public void testValidTwo() { + String testString = "madam"; + assertTrue(palindromeChecker.checkPalindrome(testString)); + } + + @Test + public void testInvalidTwo() { + String testString = "pantry"; + assertFalse(palindromeChecker.checkPalindrome(testString)); + } + + @Test + public void testValidThree() { + String testString = "RaDar"; + assertTrue(palindromeChecker.checkPalindrome(testString)); + } + + @Test + public void testInvalidThree() { + String testString = "Win"; + assertFalse(palindromeChecker.checkPalindrome(testString)); + } + + @Test + public void testBlankString() { + String testString = ""; + assertTrue(palindromeChecker.checkPalindrome(testString)); + } + + @Test + public void testStringWithNumbers() { + String testString = "12321"; + assertTrue(palindromeChecker.checkPalindrome(testString)); + } + + @Test + public void testStringWithNumbersTwo() { + String testString = "12325"; + assertFalse(palindromeChecker.checkPalindrome(testString)); + } + + @Test + public void testStringWithNumbersAndLetters() { + String testString = "po454op"; + assertTrue(palindromeChecker.checkPalindrome(testString)); + } +}