diff --git a/curriculum/challenges/english/10-coding-interview-prep/project-euler/problem-38-pandigital-multiples.md b/curriculum/challenges/english/10-coding-interview-prep/project-euler/problem-38-pandigital-multiples.md
index e0ccd868bb..e385d29d0f 100644
--- a/curriculum/challenges/english/10-coding-interview-prep/project-euler/problem-38-pandigital-multiples.md
+++ b/curriculum/challenges/english/10-coding-interview-prep/project-euler/problem-38-pandigital-multiples.md
@@ -10,30 +10,36 @@ dashedName: problem-38-pandigital-multiples
Take the number 192 and multiply it by each of 1, 2, and 3:
-
- 192 × 1 = 192
- 192 × 2 = 384
- 192 × 3 = 576
-
+$$\begin{align}
+ 192 × 1 = 192\\\\
+ 192 × 2 = 384\\\\
+ 192 × 3 = 576\\\\
+\end{align}$$
By concatenating each product we get the 1 to 9 pandigital, 192384576. We will call 192384576 the concatenated product of 192 and (1, 2, 3).
The same can be achieved by starting with 9 and multiplying by 1, 2, 3, 4, and 5, giving the pandigital, 918273645, which is the concatenated product of 9 and (1, 2, 3, 4, 5).
-What is the largest 1 to 9 pandigital 9-digit number that can be formed as the concatenated product of an integer with (1, 2, ... , `n`) where `n` > 1?
+What is the largest 1 to `k` pandigital `k`-digit number that can be formed as the concatenated product of an integer with (1, 2, ..., `n`) where `n` > 1?
# --hints--
-`pandigitalMultiples()` should return a number.
+`pandigitalMultiples(8)` should return a number.
```js
-assert(typeof pandigitalMultiples() === 'number');
+assert(typeof pandigitalMultiples(8) === 'number');
```
-`pandigitalMultiples()` should return 932718654.
+`pandigitalMultiples(8)` should return `78156234`.
```js
-assert.strictEqual(pandigitalMultiples(), 932718654);
+assert.strictEqual(pandigitalMultiples(8), 78156234);
+```
+
+`pandigitalMultiples(9)` should return `932718654`.
+
+```js
+assert.strictEqual(pandigitalMultiples(9), 932718654);
```
# --seed--
@@ -41,38 +47,37 @@ assert.strictEqual(pandigitalMultiples(), 932718654);
## --seed-contents--
```js
-function pandigitalMultiples() {
+function pandigitalMultiples(k) {
return true;
}
-pandigitalMultiples();
+pandigitalMultiples(8);
```
# --solutions--
```js
-function pandigitalMultiples() {
-
- function get9DigitConcatenatedProduct(num) {
- // returns false if concatenated product is not 9 digits
+function pandigitalMultiples(k) {
+ function getKDigitConcatenatedProduct(num, k) {
+ // returns false if concatenated product is not k digits
let concatenatedProduct = num.toString();
- for (let i = 2; concatenatedProduct.length < 9; i++) {
+ for (let i = 2; concatenatedProduct.length < k; i++) {
concatenatedProduct += num * i;
}
- return concatenatedProduct.length === 9 ? concatenatedProduct : false;
+ return concatenatedProduct.length === k ? concatenatedProduct : false;
}
- function is1to9Pandigital(num) {
+ function is1toKPandigital(num, k) {
const numStr = num.toString();
- // check if length is not 9
- if (numStr.length !== 9) {
+ // check if length is not k
+ if (numStr.length !== k) {
return false;
}
// check if pandigital
- for (let i = 9; i > 0; i--) {
+ for (let i = k; i > 0; i--) {
if (numStr.indexOf(i.toString()) === -1) {
return false;
}
@@ -81,11 +86,13 @@ function pandigitalMultiples() {
}
let largestNum = 0;
- for (let i = 9999; i >= 9000; i--) {
- const concatenatedProduct = get9DigitConcatenatedProduct(i);
- if (is1to9Pandigital(concatenatedProduct) && concatenatedProduct > largestNum) {
- largestNum = parseInt(concatenatedProduct);
- break;
+ for (let i = 10 ** Math.floor(k / 2) + 1; i >= 1; i--) {
+ const concatenatedProduct = getKDigitConcatenatedProduct(i, k);
+ if (is1toKPandigital(concatenatedProduct, k)) {
+ const number = parseInt(concatenatedProduct, 10);
+ if (number > largestNum) {
+ largestNum = number;
+ }
}
}
return largestNum;