Fixed typos and added a reference. (#27451)

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Andrew Mackie 2019-03-03 08:14:07 -08:00 committed by Randell Dawson
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title: Graphs
---
## Graphs
A graph is a data-structure you can use to solve routing problems, such as "Are these two components connected?" and "What is the shortest path from point a to b?"
A graph is a data structure you can use to solve routing problems, such as "Are these two components connected?" and "What is the shortest path from point a to point b?"
A graph consists of nodes and edges.
A node (i.e. vertex) is an object in your graph.
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If two nodes are connected by an edge, they are neighbours (i.e. adjacent).
Depending on the problem you can use either two-way (undirected) or one-way (directed) edges.
If you have a undirected edge from a to b, there is also a way from b to a.
If you have a directed edge from a to b, there is not necessarily an edge from b to a.
If you have an undirected edge from a to b, there is also a way from b to a.
If you have a directed edge from a to b, there is not necessarily a way from b to a (as this would require a separate directed edge from b to a, which may not exist).
You can use graphs to formulate situations such as:
* Geographical maps
* Each city in your country is a node
* If two cities are connected by a road there is a edge between them
* If two cities are connected by a road there is an edge between them
* Roads can be one- or two-way (both directed and undirected edges)
* the weight can be the lenght of the road
* The weight can be the length of the road
* Flow of water
* Each floodgate is a node
* Each canal is an edge
* water will only flow in one direction so the edges are directed
* the weight can be the maximum water capacity of the flow
* Water will only flow in one direction so the edges are directed
* The weight can be the maximum water capacity of the flow
Example: a graph that has as nodes the capitals of the Nordic countries, and as (undirected) edges the driving distance to cities connected by direct road.
Example: a graph that has as nodes the capitals of the Nordic countries, and as (undirected) edges the driving distance to the cities connected by a direct road.
```
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. |Reykjavik|
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#### More Information:
<!-- Please add any articles you think might be helpful to read before writing the article -->
[Wikipedia](https://en.wikipedia.org/wiki/Graph_(discrete_mathematics))
<a href='https://github.com/freecodecamp/guides/tree/master/src/pages/algorithms/graph-algorithms/breadth-first-search/index.md' target='_blank' rel='nofollow'>Breadth First Search (BFS)</a>
<a href='https://github.com/freecodecamp/guides/tree/master/src/pages/algorithms/graph-algorithms/depth-first-search/index.md' target='_blank' rel='nofollow'>Depth First Search (DFS)</a>