freeCodeCamp/curriculum/challenges/english/10-coding-interview-prep/data-structures/create-a-set-class.md

---
id: 8d1323c8c441eddfaeb5bdef
title: Create a Set Class
challengeType: 1
forumTopicId: 301632
---

## Description
<section id='description'>

In this exercise we are going to create a class named <code>Set</code> to emulate an abstract data structure called "set". A set is like an array, but it cannot contain duplicate values. The typical use for a set is to simply check for the presence of an item.
We can see how the ES6 <code>Set</code> object works in the example below:

```js
const set1 = new Set([1, 2, 3, 5, 5, 2, 0]);
console.log(set1);
// output: {1, 2, 3, 5, 0}
console.log(set1.has(1));
// output: true
console.log(set1.has(6));
// output: false
```

First, we will create an add method that adds a value to our set collection as long as the value does not already exist in the set.
Then we will create a remove method that removes a value from the set collection if it already exists.
And finally, we will create a size method that returns the number of elements inside the set collection.
</section>

## Instructions
<section id='instructions'>

Create an <code>add</code> method that adds a unique value to the set collection and returns <code>true</code> if the value was successfully added and <code>false</code> otherwise.

Create a <code>remove</code> method that accepts a value and checks if it exists in the set. If it does, then this method should remove it from the set collection, and return <code>true</code>. Otherwise, it should return <code>false</code>.
Create a <code>size</code> method that returns the size of the set collection.
</section>


## Tests
<section id='tests'>

```yml
tests:
  - text: Your <code>Set</code> class should have an <code>add</code> method.
    testString: assert((function(){var test = new Set(); return (typeof test.add === 'function')}()));
  - text: Your <code>add</code> method should not add duplicate values.
    testString: assert((function(){var test = new Set(); test.add('a'); test.add('b'); test.add('a'); var vals = test.values(); return (vals[0] === 'a' && vals[1] === 'b' && vals.length === 2)}()));
  - text: Your <code>add</code> method should return <code>true</code> when a value has been successfully added.
    testString: assert((function(){var test = new Set(); var result = test.add('a'); return (result != undefined) && (result === true);}()));
  - text: Your <code>add</code> method should return <code>false</code> when a duplicate value is added.
    testString: assert((function(){var test = new Set(); test.add('a'); var result = test.add('a'); return (result != undefined) && (result === false);}()));
  - text: Your <code>Set</code> class should have a <code>remove</code> method.
    testString: assert((function(){var test = new Set(); return (typeof test.remove === 'function')}()));
  - text: Your <code>remove</code> method should only remove items that are present in the set.
    testString: assert.deepEqual((function(){var test = new Set(); test.add('a');test.add('b');test.remove('c'); return test.values(); })(), ['a', 'b']);
  - text: Your <code>remove</code> method should remove the given item from the set.
    testString: assert((function(){var test = new Set(); test.add('a');test.add('b');test.remove('a'); var vals = test.values(); return (vals[0] === 'b' && vals.length === 1)}()));
  - text: Your <code>Set</code> class should have a <code>size</code> method.
    testString: assert((function(){var test = new Set(); return (typeof test.size === 'function')}()));
  - text: The <code>size</code> method should return the number of elements in the collection.
    testString: assert((function(){var test = new Set(); test.add('a');test.add('b');test.remove('a');return (test.size() === 1)}()));

```

</section>

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

<div id='js-seed'>

```js
class Set {
  constructor() {
    // Dictionary will hold the items of our set
    this.dictionary = {};
    this.length = 0;
  }

  // This method will check for the presence of an element and return true or false
  has(element) {
    return this.dictionary[element] !== undefined;
  }

  // This method will return all the values in the set
  values() {
    return Object.keys(this.dictionary);
  }

  // Only change code below this line
  
  // Only change code above this line
}
```

</div>
</section>

## Solution
<section id='solution'>


```js
class Set {
  constructor() {
    this.dictionary = {};
    this.length = 0;
  }

  has(element) {
    return this.dictionary[element] !== undefined;
  }

  values() {
    return Object.keys(this.dictionary);
  }

  add(element) {
    if (!this.has(element)) {
      this.dictionary[element] = true;
      this.length++;
      return true;
    }

    return false;
  }

  remove(element) {
    if (this.has(element)) {
      delete this.dictionary[element];
      this.length--;
      return true;
    }

    return false;
  }

  size() {
    return this.length;
  }
}
```

</section>