feat: Added Solution to Euler Problem 4

Project-Euler/Problem4.js

@@ -0,0 +1,38 @@
+// 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, n, m, d, inf, sup, limit, number = 0;
+  for (i = 1; i < digits; i++) {
+    number = 10 * number + 9; //
+  }
+  inf = number; // highest (digits - 1) number, in this example highest 2 digit number
+  sup = 10 * number + 9; // highest (digits) number, in this example highest 3 digit number
+
+  function isPalindromic(n) {
+    let p = 0, q = n, r;
+    while (n > 0) {
+      r = n % 10;
+      p = 10 * p + r;
+      n = Math.floor(n / 10);
+    }
+    return p === q; // returning whether the number is palindromic or not
+  }
+
+  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;
+      }
+    }
+  }
+  return NaN; // returning not a number, if any such case arise
+}
+
+console.log(largestPalindromic(3));