freeCodeCamp/curriculum/challenges/english/08-coding-interview-prep/rosetta-code/cusip.md

---
id: 5a23c84252665b21eecc7e05
title: CUSIP
challengeType: 5
---

## Description
<section id='description'>
A <b>CUSIP</b> is a nine-character alphanumeric code that identifies a North American financial security for the purposes of facilitating clearing and settlement of trades. The CUSIP was adopted as an American National Standard under Accredited Standards X9.6.
Write a function that takes a string as a parameter and checks if the string is valid CUSIP.
</section>

## Instructions
<section id='instructions'>

</section>

## Tests
<section id='tests'>

``` yml
tests:
  - text: <code>isCusip</code> should be a function.
    testString: assert(typeof isCusip == 'function', '<code>isCusip</code> should be a function.');
  - text: <code>isCusip("037833100")</code> should return a boolean.
    testString: assert(typeof isCusip("037833100") == 'boolean', '<code>isCusip("037833100")</code> should return a boolean.');
  - text: <code>isCusip("037833100")</code> should return <code>true</code>.
    testString: assert.equal(isCusip("037833100"), true, '<code>isCusip("037833100")</code> should return <code>true</code>.');
  - text: <code>isCusip("17275R102")</code> should return <code>true</code>.
    testString: assert.equal(isCusip("17275R102"), true, '<code>isCusip("17275R102")</code> should return <code>true</code>.');
  - text: <code>isCusip("38259P50a")</code> should return <code>false</code>.
    testString: assert.equal(isCusip("38259P50a"), false, '<code>isCusip("38259P50a")</code> should return <code>false</code>.');
  - text: <code>isCusip("38259P508")</code> should return <code>true</code>.
    testString: assert.equal(isCusip("38259P508"), true, '<code>isCusip("38259P508")</code> should return <code>true</code>.');
  - text: <code>isCusip("38259P50#")</code> should return <code>false</code>.
    testString: assert.equal(isCusip("38259P50#"), false, '<code>isCusip("38259P50#")</code> should return <code>false</code>.');
  - text: <code>isCusip("68389X105")</code> should return <code>true</code>.
    testString: assert.equal(isCusip("68389X105"), true, '<code>isCusip("68389X105")</code> should return <code>true</code>.');
  - text: <code>isCusip("68389X106")</code> should return <code>false</code>.
    testString: assert.equal(isCusip("68389X106"), false, '<code>isCusip("68389X106")</code> should return <code>false</code>.');
  - text: <code>isCusip("5949181")</code> should return <code>false</code>.
    testString: assert.equal(isCusip("5949181"), false, '<code>isCusip("5949181")</code> should return <code>false</code>.');
```

</section>

## Challenge Seed
<section id='challengeSeed'>
<div id='js-seed'>

```js
function isCusip (s) {
  // Good luck!
}
```

</div>
</section>

## Solution
<section id='solution'>

```js
function isCusip (s) {
  if (s.length != 9) return false;
  var sum = 0;
  var ASCII = x => x.charCodeAt(0);
  for (var i = 0; i < 7; i++) {
    var c = s.charCodeAt(i);

    var v;
    if (c >= ASCII('0') && c <= ASCII('9')) {
      v = c - 48;
    } else if (c >= ASCII('A') && c <= ASCII('Z')) {
      v = c - 64; // lower case letters apparently invalid
    } else if (c == ASCII('*')) {
      v = 36;
    } else if (c == ASCII('@')) {
      v = 37;
    } else if (c == ASCII('#')) {
      v = 38;
    } else {
      return false;
    }
    if (i % 2 == 1) v *= 2; // check if odd as using 0-based indexing
    sum += Math.floor(v / 10) + v % 10;
  }
  return s.charCodeAt(8) - 48 == (10 - (sum % 10)) % 10;
}
```

</section>