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Published at Apr 20 2021
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Instructions

Test suite

Solution

Insert and search for numbers in a binary tree.

When we need to represent sorted data, an array does not make a good data structure.

Say we have the array `[1, 3, 4, 5]`

, and we add 2 to it so it becomes
`[1, 3, 4, 5, 2]`

now we must sort the entire array again! We can
improve on this by realizing that we only need to make space for the new
item `[1, nil, 3, 4, 5]`

, and then adding the item in the space we
added. But this still requires us to shift many elements down by one.

Binary Search Trees, however, can operate on sorted data much more efficiently.

A binary search tree consists of a series of connected nodes. Each node
contains a piece of data (e.g. the number 3), a variable named `left`

,
and a variable named `right`

. The `left`

and `right`

variables point at
`nil`

, or other nodes. Since these other nodes in turn have other nodes
beneath them, we say that the left and right variables are pointing at
subtrees. All data in the left subtree is less than or equal to the
current node's data, and all data in the right subtree is greater than
the current node's data.

For example, if we had a node containing the data 4, and we added the data 2, our tree would look like this:

```
4
/
2
```

If we then added 6, it would look like this:

```
4
/ \
2 6
```

If we then added 3, it would look like this

```
4
/ \
2 6
\
3
```

And if we then added 1, 5, and 7, it would look like this

```
4
/ \
/ \
2 6
/ \ / \
1 3 5 7
```

Go through the setup instructions for Javascript to install the necessary dependencies:

https://exercism.io/tracks/javascript/installation

Please `cd`

into exercise directory before running all below commands.

Install assignment dependencies:

```
$ npm install
```

Execute the tests with:

```
$ npm test
```

In the test suites all tests but the first have been skipped.

Once you get a test passing, you can enable the next one by changing `xtest`

to
`test`

.

Once you have a solution ready, you can submit it using:

```
exercism submit binary-search-tree.js
```

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

Josh Cheek https://twitter.com/josh_cheek

```
import { BinarySearchTree } from './binary-search-tree';
function recordAllData(bst) {
const out = [];
bst.each((data) => out.push(data));
return out;
}
describe('BinarySearchTree', () => {
test('data is retained', () => {
expect(new BinarySearchTree(4).data).toEqual(4);
});
describe('insert data at proper node', () => {
xtest('smaller number at left node', () => {
const four = new BinarySearchTree(4);
four.insert(2);
expect(four.data).toEqual(4);
expect(four.left.data).toEqual(2);
});
xtest('same number at left node"', () => {
const four = new BinarySearchTree(4);
four.insert(4);
expect(four.data).toEqual(4);
expect(four.left.data).toEqual(4);
});
xtest('greater number at right node', () => {
const four = new BinarySearchTree(4);
four.insert(5);
expect(four.data).toEqual(4);
expect(four.right.data).toEqual(5);
});
});
xtest('can create complex tree', () => {
const four = new BinarySearchTree(4);
four.insert(2);
four.insert(6);
four.insert(1);
four.insert(3);
four.insert(5);
four.insert(7);
expect(four.data).toEqual(4);
expect(four.left.data).toEqual(2);
expect(four.left.left.data).toEqual(1);
expect(four.left.right.data).toEqual(3);
expect(four.right.data).toEqual(6);
expect(four.right.left.data).toEqual(5);
expect(four.right.right.data).toEqual(7);
});
describe('can sort data', () => {
xtest('can sort single number', () => {
expect(recordAllData(new BinarySearchTree(2))).toEqual([2]);
});
xtest('can sort if second number is smaller than first', () => {
const four = new BinarySearchTree(2);
four.insert(1);
expect(recordAllData(four)).toEqual([1, 2]);
});
xtest('can sort if second number is same as first', () => {
const four = new BinarySearchTree(2);
four.insert(2);
expect(recordAllData(four)).toEqual([2, 2]);
});
xtest('can sort if second number is greater than first', () => {
const four = new BinarySearchTree(2);
four.insert(3);
expect(recordAllData(four)).toEqual([2, 3]);
});
xtest('can sort complex tree', () => {
const four = new BinarySearchTree(2);
four.insert(1);
four.insert(3);
four.insert(6);
four.insert(7);
four.insert(5);
expect(recordAllData(four)).toEqual([1, 2, 3, 5, 6, 7]);
});
});
});
```

```
export class BinarySearchTree {
constructor(value) {
this._data = value;
this._left = null;
this._right = null;
}
get data() {
return this._data;
}
get right() {
return this._right;
}
get left() {
return this._left;
}
insert(data) {
if (data <= this._data) {
if (this._left) {
this._left.insert(data);
} else {
this._left = new BinarySearchTree(data);
}
} else {
if (this._right) {
this._right.insert(data);
} else {
this._right = new BinarySearchTree(data);
}
}
}
each(cb, node = this) {
if (node) {
this.each(cb, node._left);
cb(node.data);
this.each(cb, node._right);
}
}
}
```

A huge amount can be learned from reading other peopleâ€™s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

- What compromises have been made?
- Are there new concepts here that you could read more about to improve your understanding?

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