fix(curriculum): faster euler 32 ref solution (#61274)

curriculum/challenges/english/18-project-euler/project-euler-problems-1-to-100/problem-32-pandigital-products.md

@@ -70,45 +70,43 @@ pandigitalProducts(4);
 # --solutions--
 
 ```js
-function pandigitalProducts(n) {
-  function is1toNPandigital(n, digitStr) {
-    // check if length is n
-    if (digitStr.length !== n) {
-      return false;
-    }
-    // check if pandigital
-    for (let i = digitStr.length; i > 0; i--) {
-      if (digitStr.indexOf(i.toString()) === -1) {
-        return false;
-      }
-    }
-    return true;
-  }
-  function concatenateNums(...numbers) {
-    let digitStr = '';
-    for (let i = 0; i < numbers.length; i++) {
-      digitStr += numbers[i].toString();
-    }
-    return digitStr;
-  }
+// Check for pandigital number
+function isPandigital(digitStr) {
+  return digitStr
+    .split('')
+    .sort()
+    .every((c, i) => c == i + 1);
+}
 
-  const pandigitalNums = [];
-  const limit = 10 ** Math.floor(n / 2) - 1;
+// Concatenate 3 numbers
+function concatenate3Nums(a, b, c) {
+  return a.toString() + b.toString() + c.toString();
+}
+
+// Find sum of all pandigital products
+function pandigitalProducts(n) {
+  const products = [];
   let sum = 0;
-  for (let mult1 = 2; mult1 < limit; mult1++) {
-    for (let mult2 = 2; mult2 < limit; mult2++) {
-      const product = mult1 * mult2;
-      const concatenated = concatenateNums(mult1, mult2, product);
+  const max = Number(Array(n)
+    .fill(0)
+    .map((_, i) => (n - i).toString())
+    .join(''));
+  const outerLimit = Math.sqrt(max);
+
+  for (let factor1 = 2; factor1 < outerLimit; factor1++) {
+    const innerLimit = max / factor1;
+
+    for (let factor2 = factor1; factor2 < innerLimit; factor2++) {
+      const product = factor1 * factor2;
+      const concatenated = concatenate3Nums(factor1, factor2, product);
+
       if (concatenated.length > n) {
         break;
-      } else if (concatenated.length < n) {
-        continue;
-      }
-      if (
-        is1toNPandigital(n, concatenated) &&
-        !pandigitalNums.includes(product)
+      } else if (concatenated.length == n &&
+        isPandigital(concatenated) &&
+        !products.includes(product)
       ) {
-        pandigitalNums.push(product);
+        products.push(product);
         sum += product;
       }
     }