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Add graph traversal algorithms (TheAlgorithms#236)
* Add DFS algorithm * Add BFS algorithm * Update README.md
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‎Algorithms.Tests/Algorithms.Tests.csproj

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<Project Sdk="Microsoft.NET.Sdk">
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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<TargetFramework>net5.0</TargetFramework>

‎Algorithms.Tests/Graph/BreadthFirstSearchTests.cs

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using Algorithms.Graph;
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using DataStructures.Graph;
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using NUnit.Framework;
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using System.Collections.Generic;
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namespace Algorithms.Tests.Graph
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{
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public class BreadthFirstSearchTests
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{
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[Test]
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public void VisitAll_ShouldCountNumberOfVisitedVertix_ResultShouldBeTheSameAsNumberOfVerticesInGraph()
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{
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//Arrange
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var graph = new DirectedWeightedGraph<int>(10);
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var vertex1 = graph.AddVertex(1);
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var vertex2 = graph.AddVertex(20);
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var vertex3 = graph.AddVertex(40);
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var vertex4 = graph.AddVertex(40);
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graph.AddEdge(vertex1, vertex2, 1);
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graph.AddEdge(vertex2, vertex3, 1);
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graph.AddEdge(vertex2, vertex4, 1);
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graph.AddEdge(vertex4, vertex1, 1);
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var dfsSearcher = new BreadthFirstSearch<int>();
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long countOfVisitedVertices = 0;
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//Act
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dfsSearcher.VisitAll(graph, vertex1, (Vertex<int> vertex) => countOfVisitedVertices++);
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//Assert
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Assert.AreEqual(countOfVisitedVertices, graph.Count);
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}
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[Test]
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public void VisitAll_ShouldCountNumberOfVisitedVerices_TwoSeparatedGraphInOne()
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{
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//Arrange
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var graph = new DirectedWeightedGraph<int>(10);
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var vertex1 = graph.AddVertex(1);
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var vertex2 = graph.AddVertex(20);
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var vertex3 = graph.AddVertex(40);
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var vertex4 = graph.AddVertex(40);
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var vertex5 = graph.AddVertex(40);
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var vertex6 = graph.AddVertex(40);
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graph.AddEdge(vertex1, vertex2, 1);
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graph.AddEdge(vertex2, vertex3, 1);
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graph.AddEdge(vertex4, vertex5, 1);
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graph.AddEdge(vertex5, vertex6, 1);
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var dfsSearcher = new BreadthFirstSearch<int>();
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long countOfVisitedVerticesPerFirstGraph = 0;
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long countOfVisitedVerticesPerSecondGraph = 0;
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//Act
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dfsSearcher.VisitAll(graph, vertex1, (Vertex<int> vertex) => countOfVisitedVerticesPerFirstGraph++);
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dfsSearcher.VisitAll(graph, vertex4, (Vertex<int> vertex) => countOfVisitedVerticesPerSecondGraph++);
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//Assert
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Assert.AreEqual(countOfVisitedVerticesPerFirstGraph, 3);
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Assert.AreEqual(countOfVisitedVerticesPerSecondGraph, 3);
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}
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[Test]
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public void VisitAll_ReturnTheSuqenceOfVertices_ShouldBeTheSameAsExpected()
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{
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//Arrange
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var graph = new DirectedWeightedGraph<int>(10);
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var vertex1 = graph.AddVertex(1);
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var vertex2 = graph.AddVertex(20);
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var vertex3 = graph.AddVertex(40);
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var vertex4 = graph.AddVertex(40);
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var vertex5 = graph.AddVertex(40);
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graph.AddEdge(vertex1, vertex2, 1);
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graph.AddEdge(vertex1, vertex5, 1);
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graph.AddEdge(vertex2, vertex3, 1);
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graph.AddEdge(vertex2, vertex5, 1);
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graph.AddEdge(vertex2, vertex4, 1);
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var dfsSearcher = new BreadthFirstSearch<int>();
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var expectedSequenceOfVisitedVertices = new List<Vertex<int>>
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{
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vertex1,
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vertex2,
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vertex5,
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vertex3,
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vertex4
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};
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var sequenceOfVisitedVertices = new List<Vertex<int>>();
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//Act
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dfsSearcher.VisitAll(graph, vertex1, (Vertex<int> vertex) => sequenceOfVisitedVertices.Add(vertex));
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//Assert
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CollectionAssert.AreEqual(expectedSequenceOfVisitedVertices, sequenceOfVisitedVertices);
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}
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}
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}

‎Algorithms.Tests/Graph/DepthFirstSearchTests.cs

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using Algorithms.Graph;
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using DataStructures.Graph;
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using NUnit.Framework;
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using System.Collections.Generic;
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namespace Algorithms.Tests.Graph
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{
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public class DepthFirstSearchTests
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{
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[Test]
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public void VisitAll_ShouldCountNumberOfVisitedVertix_ResultShouldBeTheSameAsNumberOfVerticesInGraph()
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{
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//Arrange
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var graph = new DirectedWeightedGraph<int>(10);
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var vertex1 = graph.AddVertex(1);
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var vertex2 = graph.AddVertex(20);
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var vertex3 = graph.AddVertex(40);
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var vertex4 = graph.AddVertex(40);
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graph.AddEdge(vertex1, vertex2, 1);
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graph.AddEdge(vertex2, vertex3, 1);
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graph.AddEdge(vertex2, vertex4, 1);
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graph.AddEdge(vertex4, vertex1, 1);
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var dfsSearcher = new DepthFirstSearch<int>();
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long countOfVisitedVertices = 0;
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//Act
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dfsSearcher.VisitAll(graph, vertex1, (Vertex<int> vertex) => countOfVisitedVertices++);
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//Assert
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Assert.AreEqual(countOfVisitedVertices, graph.Count);
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}
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[Test]
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public void VisitAll_ShouldCountNumberOfVisitedVerices_TwoSeparatedGraphInOne()
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{
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//Arrange
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var graph = new DirectedWeightedGraph<int>(10);
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var vertex1 = graph.AddVertex(1);
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var vertex2 = graph.AddVertex(20);
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var vertex3 = graph.AddVertex(40);
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var vertex4 = graph.AddVertex(40);
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var vertex5 = graph.AddVertex(40);
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var vertex6 = graph.AddVertex(40);
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graph.AddEdge(vertex1, vertex2, 1);
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graph.AddEdge(vertex2, vertex3, 1);
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graph.AddEdge(vertex4, vertex5, 1);
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graph.AddEdge(vertex5, vertex6, 1);
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var dfsSearcher = new DepthFirstSearch<int>();
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long countOfVisitedVerticesPerFirstGraph = 0;
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long countOfVisitedVerticesPerSecondGraph = 0;
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//Act
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dfsSearcher.VisitAll(graph, vertex1, (Vertex<int> vertex) => countOfVisitedVerticesPerFirstGraph++);
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dfsSearcher.VisitAll(graph, vertex4, (Vertex<int> vertex) => countOfVisitedVerticesPerSecondGraph++);
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//Assert
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Assert.AreEqual(countOfVisitedVerticesPerFirstGraph, 3);
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Assert.AreEqual(countOfVisitedVerticesPerSecondGraph, 3);
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}
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[Test]
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public void VisitAll_ReturnTheSuqenceOfVertices_ShouldBeTheSameAsExpected()
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{
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//Arrange
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var graph = new DirectedWeightedGraph<int>(10);
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var vertex1 = graph.AddVertex(1);
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var vertex2 = graph.AddVertex(20);
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var vertex3 = graph.AddVertex(40);
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var vertex4 = graph.AddVertex(40);
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var vertex5 = graph.AddVertex(40);
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graph.AddEdge(vertex1, vertex2, 1);
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graph.AddEdge(vertex2, vertex3, 1);
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graph.AddEdge(vertex2, vertex4, 1);
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graph.AddEdge(vertex3, vertex5, 1);
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var dfsSearcher = new DepthFirstSearch<int>();
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var expectedSequenceOfVisitedVertices = new List<Vertex<int>>
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{
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vertex1,
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vertex2,
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vertex3,
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vertex5,
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vertex4
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};
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var sequenceOfVisitedVertices = new List<Vertex<int>>();
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//Act
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dfsSearcher.VisitAll(graph, vertex1, (Vertex<int> vertex) => sequenceOfVisitedVertices.Add(vertex));
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//Assert
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CollectionAssert.AreEqual(expectedSequenceOfVisitedVertices, sequenceOfVisitedVertices);
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}
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}
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}

‎Algorithms/Algorithms.csproj

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</ItemGroup>
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<ItemGroup>
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<ProjectReference Include="..\DataStructures\DataStructures.csproj" />
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<ProjectReference Include="..\Utilities\Utilities.csproj" />
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</ItemGroup>
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‎Algorithms/Graph/BreadthFirstSearch.cs

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using System;
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using System.Collections.Generic;
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using DataStructures.Graph;
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namespace Algorithms.Graph
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{
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/// <summary>
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/// Breadth First Search - algorithm for traversing graph.
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/// Algorithm starts from root node that is selected by the user.
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/// Algorithm explores all nodes at the present depth.
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/// </summary>
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/// <typeparam name="T">Vertex data type.</typeparam>
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public class BreadthFirstSearch<T> : IGraphSearch<T> where T : IComparable<T>
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{
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/// <summary>
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/// Traverses graph from start vertex.
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/// </summary>
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/// <param name="graph">Graph instance.</param>
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/// <param name="startVertex">Vertex that search starts from.</param>
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/// <param name="action">Action that needs to be executed on each graph vertex.</param>
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public void VisitAll(IDirectedWeightedGraph<T> graph, Vertex<T> startVertex, Action<Vertex<T>>? action = default)
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{
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Bfs(graph, startVertex, action, new HashSet<Vertex<T>>());
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}
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/// <summary>
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/// Traverses graph from start vertex.
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/// </summary>
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/// <param name="graph">Graph instance.</param>
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/// <param name="startVertex">Vertex that search starts from.</param>
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/// <param name="action">Action that needs to be executed on each graph vertex.</param>
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/// <param name="visited">Hash set with visited vertices.</param>
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private void Bfs(IDirectedWeightedGraph<T> graph, Vertex<T> startVertex, Action<Vertex<T>>? action, HashSet<Vertex<T>> visited)
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{
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var queue = new Queue<Vertex<T>>();
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queue.Enqueue(startVertex);
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while (queue.Count > 0)
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{
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var currentVertex = queue.Dequeue();
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if (currentVertex == null || visited.Contains(currentVertex))
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{
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continue;
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}
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foreach (var vertex in graph.GetNeighbors(currentVertex))
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{
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queue.Enqueue(vertex!);
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}
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action?.Invoke(currentVertex);
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visited.Add(currentVertex);
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}
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}
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}
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}

‎Algorithms/Graph/DepthFirstSearch.cs

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using System;
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using System.Collections.Generic;
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using DataStructures.Graph;
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namespace Algorithms.Graph
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{
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/// <summary>
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/// Depth First Search - algorithm for traversing graph.
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/// Algorithm starts from root node that is selected by the user.
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/// Algorithm explores as far as possible along each branch before backtracking.
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/// </summary>
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/// <typeparam name="T">Vertex data type.</typeparam>
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public class DepthFirstSearch<T> : IGraphSearch<T> where T : IComparable<T>
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{
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/// <summary>
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/// Traverses graph from start vertex.
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/// </summary>
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/// <param name="graph">Graph instance.</param>
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/// <param name="startVertex">Vertex that search starts from.</param>
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/// <param name="action">Action that needs to be executed on each graph vertex.</param>
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public void VisitAll(IDirectedWeightedGraph<T> graph, Vertex<T> startVertex, Action<Vertex<T>>? action = default)
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{
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Dfs(graph, startVertex, action, new HashSet<Vertex<T>>());
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}
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/// <summary>
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/// Traverses graph from start vertex.
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/// </summary>
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/// <param name="graph">Graph instance.</param>
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/// <param name="startVertex">Vertex that search starts from.</param>
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/// <param name="action">Action that needs to be executed on each graph vertex.</param>
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/// <param name="visited">Hash set with visited vertices.</param>
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private void Dfs(IDirectedWeightedGraph<T> graph, Vertex<T> startVertex, Action<Vertex<T>>? action, HashSet<Vertex<T>> visited)
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{
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action?.Invoke(startVertex);
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visited.Add(startVertex);
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foreach (var vertex in graph.GetNeighbors(startVertex))
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{
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if (vertex == null || visited.Contains(vertex))
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{
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continue;
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}
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Dfs(graph, vertex!, action, visited);
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}
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}
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}
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}

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