# `graph` is a generic library for creating graph data structures and performing operations on them. It supports different kinds of graphs such as directed graphs, acyclic graphs, or trees.

# Features

• Vertices of any data type, such as `int` or `City`.
• Edges with optional data, such as weights or attributes.
• Optionally combinable graph types and traits.
• Validations considering the graph type, such as cycle detection in acyclic graphs.
• Determination of graph and vertex properties, such as degree or tree-depth.
• Non-recursive walks, DFS, and BFS.
• Pathfinding algorithms, considering edge weights where appropriate:
• Hamiltonian paths and cycles
• Eulerian paths and cycles
• Shortest path (Dijkstra)
• Strongly connected components (Tarjan)
• Visualization of graphs using Graphviz.
• Extensive tests with ~90% coverage.

Status: Because `graph` is in version 0, the public API shouldn’t be considered stable.

# Getting started

``````go get github.com/dominikbraun/graph
``````

# Quick examples

## Create a graph of integers ```g := graph.New(graph.IntHash)

_ = g.AddEdge(1, 2)
_ = g.AddEdge(1, 4)
_ = g.AddEdge(2, 3)
_ = g.AddEdge(2, 4)
_ = g.AddEdge(2, 5)
_ = g.AddEdge(3, 5)```

## Create a directed acyclic graph of integers ```g := graph.New(graph.IntHash, graph.Directed(), graph.Acyclic())

_ = g.AddEdge(1, 2)
_ = g.AddEdge(1, 3)
_ = g.AddEdge(2, 3)
_ = g.AddEdge(2, 4)
_ = g.AddEdge(3, 4)```

## Create a graph of a custom type

To understand this example in detail, see the concept of hashes.

```type City struct {
Name string
}

cityHash := func(c City) string {
return c.Name
}

g := graph.New(cityHash)

## Create a weighted graph ```g := graph.New(cityHash, graph.Weighted())

_ = g.AddEdge("london", "munich", graph.EdgeWeight(3))
_ = g.AddEdge("london", "paris", graph.EdgeWeight(2))
_ = g.AddEdge("munich", "paris", graph.EdgeWeight(2))

## Perform a Depth-First Search

This example traverses and prints all vertices in the graph in DFS order. ```g := graph.New(graph.IntHash, graph.Directed())

_ = g.AddEdge(1, 2)
_ = g.AddEdge(1, 3)
_ = g.AddEdge(3, 4)

_ = graph.DFS(g, 1, func(value int) bool {
fmt.Println(value)
return false
})```
``````1 3 4 2
``````

## Find strongly connected components ```g := graph.New(graph.IntHash)

// Add vertices and edges ...

scc, _ := graph.StronglyConnectedComponents(g)

fmt.Println(scc)```
``````[[1 2 5] [3 4 8] [6 7]]
``````

## Find the shortest path ```g := graph.New(graph.StringHash, graph.Weighted())

// Add vertices and weighted edges ...

path, _ := graph.ShortestPath(g, "A", "B")

fmt.Println(path)```
``````[A C E B]
``````

## Cycle checks for acyclic graphs ```g := graph.New(graph.IntHash, graph.Acyclic())

_ = g.AddEdge(1, 2)
_ = g.AddEdge(1, 3)

if err := g.AddEdge(2, 3); err != nil {
panic(err)
}```
``````panic: an edge between 2 and 3 would introduce a cycle
``````

## Visualize a graph using Graphviz

The following example will generate a DOT description for `g` and write it into the given file.

```g := graph.New(graph.IntHash, graph.Directed())

_ = g.AddEdge(1, 2)
_ = g.AddEdge(1, 3)

file, _ := os.Create("./mygraph.gv")
_ = draw.DOT(g, file)```

To generate an SVG from the created file using Graphviz, use a command such as the following:

``````dot -Tsvg -O mygraph.gv
``````

## Setting edge attributes

Edges may have one or more attributes which can be used to store metadata. Attributes will be taken into account when visualizing a graph. For example, this edge will be rendered in red color:

`_ = g.AddEdge(1, 2, graph.EdgeAttribute("color", "red"))`

To get an overview of all supported attributes, take a look at the DOT documentation.

# Concepts

## Hashes

A graph consists of nodes (or vertices) of type `T`, which are identified by a hash value of type `K`. The hash value is obtained using the hashing function passed to `graph.New`.

### Primitive types

For primitive types such as `string` or `int`, you may use a predefined hashing function such as `graph.IntHash` – a function that takes an integer and uses it as a hash value at the same time:

`g := graph.New(graph.IntHash)`

This also means that only one vertex with a value like `5` can exist in the graph if `graph.IntHash` used.

### Custom types

For storing custom data types, you need to provide your own hashing function. This example function takes a `City` and returns the city name as an unique hash value:

```cityHash := func(c City) string {
return c.Name
}```

Creating a graph using this hashing function will yield a graph with vertices of type `City` identified by hash values of type `string`.

`g := graph.New(cityHash)`

## Traits

The behavior of a graph, for example when adding or retrieving edges, depends on its traits. You can set the graph’s traits using the functional options provided by this library:

`g := graph.New(graph.IntHash, graph.Directed(), graph.Weighted())`

# Documentation

The full documentation is available at pkg.go.dev.

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