add: isPalindrome function implementation

DIRECTORY.md

@@ -20,3 +20,6 @@
   - [QuickSort](Sorting/QuickSort.js)
   - [SelectionSort](Sorting/SelectionSort.js)
   - [ThreeNumberSort](Sorting/ThreeNumberSort.js)
+
+- **Strings**
+  - [PalindromeCheck](Strings/PalindromeCheck.js)

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 };

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);
+  });
+});