From 829fce8f11c5e06f7979618db758962e970e5e65 Mon Sep 17 00:00:00 2001
From: Elias Afara <afaraelias@gmail.com>
Date: Sun, 15 Oct 2023 23:50:10 +0200
Subject: [PATCH] add: isPalindrome function implementation

---
 DIRECTORY.md                          |  3 +++
 Strings/PalindromeCheck.js            | 25 +++++++++++++++++++++
 Strings/tests/PalindromeCheck.test.js | 31 +++++++++++++++++++++++++++
 3 files changed, 59 insertions(+)
 create mode 100644 Strings/PalindromeCheck.js
 create mode 100644 Strings/tests/PalindromeCheck.test.js

diff --git a/DIRECTORY.md b/DIRECTORY.md
index 5d14e1d..13607c7 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -20,3 +20,6 @@
   - [QuickSort](Sorting/QuickSort.js)
   - [SelectionSort](Sorting/SelectionSort.js)
   - [ThreeNumberSort](Sorting/ThreeNumberSort.js)
+
+- **Strings**
+  - [PalindromeCheck](Strings/PalindromeCheck.js)
diff --git a/Strings/PalindromeCheck.js b/Strings/PalindromeCheck.js
new file mode 100644
index 0000000..275b544
--- /dev/null
+++ b/Strings/PalindromeCheck.js
@@ -0,0 +1,25 @@
+/**
+ * Check if a given string is a palindrome.
+ *
+ * @param {string} str - The input string to be checked for palindrome.
+ * @returns {boolean} - True if the input string is a palindrome, false otherwise.
+ *
+ * @description
+ * A palindrome is a string that reads the same forwards and backwards. This function
+ * checks whether the input string is a palindrome, ignoring spaces, punctuation, and
+ * letter casing. It handles single-character strings as palindromes as well.
+ *
+ * @complexity
+ * - Time Complexity: O(n), where n is the length of the input string.
+ *   The function iterates through the string once to check for palindromic properties.
+ * - Space Complexity: O(1), as the function only uses a constant amount of extra memory.
+ */
+function isPalindrome(str) {
+  // Remove non-alphanumeric characters and convert to lowercase
+  str = str.replace(/[^a-zA-Z0-9]/g, "").toLowerCase();
+
+  // Check if the cleaned string is the same when reversed
+  return str === str.split("").reverse().join("");
+}
+
+export { isPalindrome };
diff --git a/Strings/tests/PalindromeCheck.test.js b/Strings/tests/PalindromeCheck.test.js
new file mode 100644
index 0000000..1b93b24
--- /dev/null
+++ b/Strings/tests/PalindromeCheck.test.js
@@ -0,0 +1,31 @@
+import { isPalindrome } from "../PalindromeCheck";
+
+describe("isPalindrome", () => {
+  it("returns true for a valid palindrome", () => {
+    expect(isPalindrome("racecar")).toBe(true);
+  });
+
+  it("returns true for a single character", () => {
+    expect(isPalindrome("a")).toBe(true);
+  });
+
+  it("returns true for an empty string", () => {
+    expect(isPalindrome("")).toBe(true);
+  });
+
+  it("returns false for a non-palindrome", () => {
+    expect(isPalindrome("hello")).toBe(false);
+  });
+
+  it("ignores spaces and punctuation", () => {
+    expect(isPalindrome("A man, a plan, a canal, Panama")).toBe(true);
+  });
+
+  it("handles letter casing", () => {
+    expect(isPalindrome("RacECar")).toBe(true);
+  });
+
+  it("returns false for a non-palindrome with spaces", () => {
+    expect(isPalindrome("not a palindrome")).toBe(false);
+  });
+});