92 lines
2.4 KiB
Markdown
92 lines
2.4 KiB
Markdown
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---
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id: 587d8256367417b2b2512c77
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title: Adjacency List
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challengeType: 1
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forumTopicId: 301620
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dashedName: adjacency-list
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---
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# --description--
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Graphs can be represented in different ways. Here we describe one way, which is called an <dfn>adjacency list</dfn>. An adjacency list is essentially a bulleted list where the left side is the node and the right side lists all the other nodes it's connected to. Below is a representation of an adjacency list.
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<blockquote>Node1: Node2, Node3<br>Node2: Node1<br>Node3: Node1</blockquote>
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Above is an undirected graph because `Node1` is connected to `Node2` and `Node3`, and that information is consistent with the connections `Node2` and `Node3` show. An adjacency list for a directed graph would mean each row of the list shows direction. If the above was directed, then `Node2: Node1` would mean there the directed edge is pointing from `Node2` towards `Node1`. We can represent the undirected graph above as an adjacency list by putting it within a JavaScript object.
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```js
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var undirectedG = {
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Node1: ["Node2", "Node3"],
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Node2: ["Node1"],
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Node3: ["Node1"]
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};
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```
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This can also be more simply represented as an array where the nodes just have numbers rather than string labels.
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```js
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var undirectedGArr = [
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[1, 2], // Node1
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[0], // Node2
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[0] // Node3
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];
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```
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# --instructions--
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Create a social network as an undirected graph with 4 nodes/people named `James`, `Jill`, `Jenny`, and `Jeff`. There are edges/relationships between James and Jeff, Jill and Jenny, and Jeff and Jenny.
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# --hints--
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`undirectedAdjList` should only contain four nodes.
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```js
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assert(Object.keys(undirectedAdjList).length === 4);
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```
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There should be an edge between `Jeff` and `James`.
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```js
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assert(
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undirectedAdjList.James.indexOf('Jeff') !== -1 &&
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undirectedAdjList.Jeff.indexOf('James') !== -1
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);
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```
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There should be an edge between `Jill` and `Jenny`.
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```js
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assert(
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undirectedAdjList.Jill.indexOf('Jenny') !== -1 &&
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undirectedAdjList.Jill.indexOf('Jenny') !== -1
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);
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```
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There should be an edge between `Jeff` and `Jenny`.
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```js
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assert(
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undirectedAdjList.Jeff.indexOf('Jenny') !== -1 &&
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undirectedAdjList.Jenny.indexOf('Jeff') !== -1
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);
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```
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# --seed--
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## --seed-contents--
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```js
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var undirectedAdjList = {};
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```
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# --solutions--
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```js
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var undirectedAdjList = {
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James: ['Jeff'],
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Jill: ['Jenny'],
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Jenny: ['Jill', 'Jeff'],
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Jeff: ['James', 'Jenny']
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};
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```
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