feat: ✨ largest palindrome from product of x numbers

apps/euler-project/src/problems/palindrome-product.ts

@@ -0,0 +1,24 @@
+export const isPalindrome = (number: number): boolean => {
+  const numberToString = number.toString();
+  return numberToString === numberToString.split('').reverse().join('');
+};
+
+export const largestPalindromeFromProductOfXNumbers = (x: number): number => {
+  if (x < 1) {
+    throw new Error('x must be greater than 0');
+  }
+  const palindromeRange = Number(new Array(x).fill(9).join().replace(/,/g, ''));
+  const isPalindromeLowestBound = Number(
+    '1' + palindromeRange.toString().slice(1, -1)
+  );
+  let largestPalindrome = 0;
+  for (let i = palindromeRange; i >= isPalindromeLowestBound; i--) {
+    for (let j = i; j >= isPalindromeLowestBound; j--) {
+      const product = i * j;
+      if (isPalindrome(product) && product > largestPalindrome) {
+        largestPalindrome = product;
+      }
+    }
+  }
+  return largestPalindrome;
+};

apps/euler-project/src/specs/largest-prime-factor.spec.ts

@@ -7,7 +7,6 @@ import { checkLargestPrimeFactor } from '../problems/largest-prime-factor';
 
 describe('largest prime factor', () => {
   it('should return largest prime factor', () => {
-    console.log(checkLargestPrimeFactor(13195));
     expect(checkLargestPrimeFactor(13195)).toEqual(29);
     expect(checkLargestPrimeFactor(600851475143)).toEqual(6857);
   });

apps/euler-project/src/specs/palindrome-product.spec.ts

@@ -0,0 +1,21 @@
+/*
+ * A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 x 99.
+ * Find the largest palindrome made from the product of two 3-digit numbers.
+ */
+
+import { largestPalindromeFromProductOfXNumbers } from '../problems/palindrome-product';
+
+describe('Largest palindrome from product of three numbers', () => {
+  it('should return a Palindrome of 9009 when x = 2', () => {
+    // Warning Slow Process beyond 3 numbers which is equivalent to inverse looping from 999 to 99
+    expect(largestPalindromeFromProductOfXNumbers(2)).toBe(9009);
+  });
+  it('should return a Palindrome of 906609 when x = 3', () => {
+    // Warning Slow Process beyond 3 numbers which is equivalent to inverse looping from 999 to 99
+    expect(largestPalindromeFromProductOfXNumbers(3)).toBe(906609);
+  });
+  it.skip('should return a Palindrome of 99000099 when x = 4', () => {
+    // Warning Slow Process beyond 3 numbers which is equivalent to inverse looping from 999 to 99
+    expect(largestPalindromeFromProductOfXNumbers(4)).toBe(99000099);
+  });
+});