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Feat: add new Markdown parser (#39800)

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and change all the challenges to new `md` format.
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Oliver Eyton-Williams
2020-11-27 19:02:05 +01:00
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curriculum/challenges/english/10-coding-interview-prep/rosetta-code/hash-join.md
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@ -1,25 +1,28 @@
---
title: Hash join
id: 5956795bc9e2c415eb244de1
title: Hash join
challengeType: 5
forumTopicId: 302284
---
## Description
<section id='description'>
An <a href="https://en.wikipedia.org/wiki/Join_(SQL)#Inner_join" title="wp: Join_(SQL)#Inner_join" target="_blank">inner join</a> is an operation that combines two data tables into one table, based on matching column values. The simplest way of implementing this operation is the <a href="https://en.wikipedia.org/wiki/Nested loop join" title="wp: Nested loop join" target="_blank">nested loop join</a> algorithm, but a more scalable alternative is the <a href="https://en.wikipedia.org/wiki/hash join" title="wp: hash join" target="_blank">hash join</a> algorithm.
# --description--
An [inner join](https://en.wikipedia.org/wiki/Join_(SQL)#Inner_join "wp: Join\_(SQL)#Inner_join") is an operation that combines two data tables into one table, based on matching column values. The simplest way of implementing this operation is the [nested loop join](<https://en.wikipedia.org/wiki/Nested loop join> "wp: Nested loop join") algorithm, but a more scalable alternative is the [hash join](<https://en.wikipedia.org/wiki/hash join> "wp: hash join") algorithm.
The "hash join" algorithm consists of two steps:
<ol>
<li><strong>Hash phase:</strong> Create a <a href="https://en.wikipedia.org/wiki/Multimap" title="wp: Multimap" target="_blank">multimap</a> from one of the two tables, mapping from each join column value to all the rows that contain it.</li>
<li><strong>Hash phase:</strong> Create a <a href='https://en.wikipedia.org/wiki/Multimap' title='wp: Multimap' target='_blank'>multimap</a> from one of the two tables, mapping from each join column value to all the rows that contain it.</li>
<ul>
<li>The multimap must support hash-based lookup which scales better than a simple linear search, because that's the whole point of this algorithm.</li>
<li>Ideally we should create the multimap for the smaller table, thus minimizing its creation time and memory size.</li>
</ul>
<li><strong>Join phase:</strong> Scan the other table, and find matching rows by looking in the multimap created before.</li>
</ol>
In pseudo-code, the algorithm could be expressed as follows:
<pre>
<strong>let</strong> <i>A</i> = the first input table (or ideally, the larger one)
<pre><strong>let</strong> <i>A</i> = the first input table (or ideally, the larger one)
<strong>let</strong> <i>B</i> = the second input table (or ideally, the smaller one)
<strong>let</strong> <i>j<sub>A</sub></i> = the join column ID of table <i>A</i>
<strong>let</strong> <i>j<sub>B</sub></i> = the join column ID of table <i>B</i>
@ -32,10 +35,8 @@ In pseudo-code, the algorithm could be expressed as follows:
<strong>let</strong> <i>c</i> = the concatenation of row <i>a</i> and row <i>b</i>
<strong>place</strong> row <i>c</i> in table <i>C</i>
</pre>
</section>
## Instructions
<section id='instructions'>
# --instructions--
Implement the "hash join" algorithm as a function and demonstrate that it passes the test-case listed below. The function should accept two arrays of objects and return an array of combined objects.
@ -127,51 +128,35 @@ Implement the "hash join" algorithm as a function and demonstrate that it passes
<h4><strong>Output</strong></h4>
|A_age|A_name|B_character|B_nemesis|
|--- |--- |--- |--- |
|27|Jonah|Jonah|Whales|
|27|Jonah|Jonah|Spiders|
|18|Alan|Alan|Ghosts|
|18|Alan|Alan|Zombies|
|28|Glory|Glory|Buffy|
|28|Alan|Alan|Ghosts|
|28|Alan|Alan|Zombies|
| A_age | A_name | B_character | B_nemesis |
| ----- | ------ | ----------- | --------- |
| 27 | Jonah | Jonah | Whales |
| 27 | Jonah | Jonah | Spiders |
| 18 | Alan | Alan | Ghosts |
| 18 | Alan | Alan | Zombies |
| 28 | Glory | Glory | Buffy |
| 28 | Alan | Alan | Ghosts |
| 28 | Alan | Alan | Zombies |
The order of the rows in the output table is not significant.
</section>
# --hints--
## Tests
<section id='tests'>
```yml
tests:
- text: <code>hashJoin</code> should be a function.
testString: assert(typeof hashJoin === 'function');
- text: '<code>hashJoin([{ age: 27, name: "Jonah" }, { age: 18, name: "Alan" }, { age: 28, name: "Glory" }, { age: 18, name: "Popeye" }, { age: 28, name: "Alan" }], [{ character: "Jonah", nemesis: "Whales" }, { character: "Jonah", nemesis: "Spiders" }, { character: "Alan", nemesis: "Ghosts" }, { character:"Alan", nemesis: "Zombies" }, { character: "Glory", nemesis: "Buffy" }, { character: "Bob", nemesis: "foo" }])</code> should return <code>[{"A_age": 27,"A_name": "Jonah", "B_character": "Jonah", "B_nemesis": "Whales"}, {"A_age": 27,"A_name": "Jonah", "B_character": "Jonah", "B_nemesis": "Spiders"}, {"A_age": 18,"A_name": "Alan", "B_character": "Alan", "B_nemesis": "Ghosts"}, {"A_age": 18,"A_name": "Alan", "B_character": "Alan", "B_nemesis": "Zombies"}, {"A_age": 28,"A_name": "Glory", "B_character": "Glory", "B_nemesis": "Buffy"}, {"A_age": 28,"A_name": "Alan", "B_character": "Alan", "B_nemesis": "Ghosts"}, {"A_age": 28,"A_name": "Alan", "B_character": "Alan", "B_nemesis": "Zombies"}]</code>'
testString: assert.deepEqual(hashJoin(hash1, hash2), res);
```
</section>
## Challenge Seed
<section id='challengeSeed'>
<div id='js-seed'>
`hashJoin` should be a function.
```js
function hashJoin(hash1, hash2) {
return [];
}
assert(typeof hashJoin === 'function');
```
</div>
`hashJoin([{ age: 27, name: "Jonah" }, { age: 18, name: "Alan" }, { age: 28, name: "Glory" }, { age: 18, name: "Popeye" }, { age: 28, name: "Alan" }], [{ character: "Jonah", nemesis: "Whales" }, { character: "Jonah", nemesis: "Spiders" }, { character: "Alan", nemesis: "Ghosts" }, { character:"Alan", nemesis: "Zombies" }, { character: "Glory", nemesis: "Buffy" }, { character: "Bob", nemesis: "foo" }])` should return `[{"A_age": 27,"A_name": "Jonah", "B_character": "Jonah", "B_nemesis": "Whales"}, {"A_age": 27,"A_name": "Jonah", "B_character": "Jonah", "B_nemesis": "Spiders"}, {"A_age": 18,"A_name": "Alan", "B_character": "Alan", "B_nemesis": "Ghosts"}, {"A_age": 18,"A_name": "Alan", "B_character": "Alan", "B_nemesis": "Zombies"}, {"A_age": 28,"A_name": "Glory", "B_character": "Glory", "B_nemesis": "Buffy"}, {"A_age": 28,"A_name": "Alan", "B_character": "Alan", "B_nemesis": "Ghosts"}, {"A_age": 28,"A_name": "Alan", "B_character": "Alan", "B_nemesis": "Zombies"}]`
```js
assert.deepEqual(hashJoin(hash1, hash2), res);
```
### After Test
<div id='js-teardown'>
# --seed--
## --after-user-code--
```js
const hash1 = [
@ -205,13 +190,16 @@ const bench1 = [{ name: 'u2v7v', num: 1 }, { name: 'n53c8', num: 10 }, { name: '
const bench2 = [{ friend: 'o8b', num: 8 }, { friend: 'ye', num: 2 }, { friend: '32i', num: 5 }, { friend: 'uz', num: 3 }, { friend: 'a5k', num: 4 }, { friend: 'uad', num: 7 }, { friend: '3w5', num: 10 }, { friend: 'vw', num: 10 }, { friend: 'ah', num: 4 }, { friend: 'qv', num: 7 }, { friend: 'ozv', num: 2 }, { friend: '9ri', num: 10 }, { friend: '7nu', num: 4 }, { friend: 'w3', num: 9 }, { friend: 'tgp', num: 8 }, { friend: 'ibs', num: 1 }, { friend: 'ss7', num: 6 }, { friend: 'g44', num: 9 }, { friend: 'tab', num: 9 }, { friend: 'zem', num: 10 }];
```
</div>
## --seed-contents--
</section>
```js
function hashJoin(hash1, hash2) {
## Solution
<section id='solution'>
return [];
}
```
# --solutions--
```js
function hashJoin(hash1, hash2) {
@ -245,8 +233,4 @@ function hashJoin(hash1, hash2) {
return hJoin(hash1, hash2, 'name=character');
}
```
</section>