---
id: 5900f3bb1000cf542c50fece
challengeType: 5
title: 'Problem 79: Passcode derivation'
---

## Description
<section id='description'>
A common security method used for online banking is to ask the user for three random characters from a passcode. For example, if the passcode was 531278, they may ask for the 2nd, 3rd, and 5th characters; the expected reply would be: 317.
The text file, keylog.txt, contains fifty successful login attempts.
Given that the three characters are always asked for in order, analyse the file so as to determine the shortest possible secret passcode of unknown length.
</section>

## Instructions
<section id='instructions'>

</section>

## Tests
<section id='tests'>

```yml
tests:
  - text: <code>euler79()</code> should return 73162890.
    testString: assert.strictEqual(euler79(), 73162890, '<code>euler79()</code> should return 73162890.');

```

</section>

## Challenge Seed
<section id='challengeSeed'>

<div id='js-seed'>

```js
function euler79() {
  // Good luck!
  return true;
}

euler79();
```

</div>



</section>

## Solution
<section id='solution'>

```js
// solution required
```
</section>
