Add Problem4 (Largest Palindrome Product)

Project-Euler/Problem4.js

@@ -1,46 +1,30 @@
-// https://projecteuler.net/problem=4
-/* A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99.
-   Find the largest palindrome made from the product of two 3-digit numbers.
-*/
-const largestPalindromic = (digits) => {
-  let i
-  let n
-  let m
-  let d
-  let limit
-  let number = 0
+function isPalindrome (number) {
+  // just 2 random names for variables!
+  const look = String(number)
+  let hear = false
 
-  for (i = 1; i < digits; i++) {
-    number = 10 * number + 9
-  }
-  const inf = number // highest (digits - 1) number, in this example highest 2 digit number
-  const sup = 10 * number + 9 // highest (digits) number, in this example highest 3 digit number
-
-  const isPalindromic = (n) => {
-    let p = 0
-    const q = n
-    let r
-    while (n > 0) {
-      r = n % 10
-      p = 10 * p + r
-      n = Math.floor(n / 10)
+  for (let i = 0; i < look.length; i++) {
+    if (look[i] === look[(look.length) - (i + 1)]) {
+      hear = true
+    } else {
+      return false
     }
-    return p === q // returning whether the number is palindromic or not
   }
+  return hear
+}
+
+function largestPalindromeProduct (n) {
+  let product = 0
+  let largestPalindrome = 11
 
-  for (n = sup * sup, m = inf * inf; n > m; n--) {
-    if (isPalindromic(n)) {
-      limit = Math.ceil(Math.sqrt(n))
-      d = sup
-      while (d >= limit) {
-        if (n % d === 0 && n / d > inf) {
-          return n
-        }
-        d -= 1
-      }
+  for (let i = 10 ** (n - 1); i < 10 ** n; i++) {
+    for (let j = 10 ** (n - 1); j < 10 ** n; j++) {
+      product = i * j
+      if (isPalindrome(product) && product > largestPalindrome) { largestPalindrome = product }
     }
   }
-  return NaN // returning not a number, if any such case arise
+  return largestPalindrome
 }
 
-console.log(largestPalindromic(3))
+console.log(isPalindrome(9009))
+console.log(largestPalindromeProduct(2))