Add graph.

Author: trekhleb

Diff for: .eslintrc

@@ -8,6 +8,7 @@
   "rules": {
     "no-bitwise": "off",
     "no-lonely-if": "off",
-    "class-methods-use-this": "off"
+    "class-methods-use-this": "off",
+    "arrow-body-style": "off"
   }
 }

Diff for: README.md

@@ -15,6 +15,7 @@
 8. [Tree](https://github.com/trekhleb/javascript-algorithms/tree/master/src/data-structures/tree)
     * [Binary Search Tree](https://github.com/trekhleb/javascript-algorithms/tree/master/src/data-structures/tree/binary-search-tree)
     * [AVL Tree](https://github.com/trekhleb/javascript-algorithms/tree/master/src/data-structures/tree/avl-tree)
+9. [Graph](https://github.com/trekhleb/javascript-algorithms/tree/master/src/data-structures/graph)
 
 ## [Algorithms](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms)
 

Diff for: src/data-structures/graph/Graph.js

@@ -0,0 +1,88 @@
+export default class Graph {
+  /**
+   * @param isDirected {boolean}
+   */
+  constructor(isDirected = false) {
+    this.vertices = {};
+    this.isDirected = isDirected;
+  }
+
+  /**
+   * @param newVertex {GraphVertex}
+   * @returns {Graph}
+   */
+  addVertex(newVertex) {
+    this.vertices[newVertex.getKey()] = newVertex;
+
+    return this;
+  }
+
+  /**
+   * @param vertexKey {string}
+   * @returns GraphVertex
+   */
+  getVertexByKey(vertexKey) {
+    return this.vertices[vertexKey];
+  }
+
+  /**
+   * @param edge {GraphEdge}
+   * @returns {Graph}
+   */
+  addEdge(edge) {
+    // Try to find and end start vertices.
+    let startVertex = this.getVertexByKey(edge.startVertex.getKey());
+    let endVertex = this.getVertexByKey(edge.endVertex.getKey());
+
+    // Insert start vertex if it wasn't inserted.
+    if (!startVertex) {
+      this.addVertex(edge.startVertex);
+      startVertex = this.getVertexByKey(edge.startVertex.getKey());
+    }
+
+    // Insert end vertex if it wasn't inserted.
+    if (!endVertex) {
+      this.addVertex(edge.endVertex);
+      endVertex = this.getVertexByKey(edge.endVertex.getKey());
+    }
+
+    // @TODO: Check if edge has been already added.
+
+    // Add edge to the vertices.
+    if (this.isDirected) {
+      // If graph IS directed then add the edge only to start vertex.
+      startVertex.addEdge(edge);
+    } else {
+      // If graph ISN'T directed then add the edge to both vertices.
+      startVertex.addEdge(edge);
+      endVertex.addEdge(edge);
+    }
+
+    return this;
+  }
+
+  /**
+   * @param startVertex {GraphVertex}
+   * @param endVertex {GraphVertex}
+   */
+  findEdge(startVertex, endVertex) {
+    const vertex = this.getVertexByKey(startVertex.getKey());
+    return vertex.findEdge(endVertex);
+  }
+
+  /**
+   * @param vertexKey {string}
+   * @returns {GraphVertex}
+   */
+  findVertexByKey(vertexKey) {
+    if (this.vertices[vertexKey]) {
+      return this.vertices[vertexKey];
+    }
+
+    return null;
+  }
+
+  toString() {
+    return Object.keys(this.vertices).toString();
+  }
+}

Diff for: src/data-structures/graph/GraphEdge.js

@@ -0,0 +1,12 @@
+export default class GraphEdge {
+  /**
+   * @param startVertex {GraphVertex}
+   * @param endVertex {GraphVertex}
+   * @param weight {number}
+   */
+  constructor(startVertex, endVertex, weight = 1) {
+    this.startVertex = startVertex;
+    this.endVertex = endVertex;
+    this.weight = weight;
+  }
+}

Diff for: src/data-structures/graph/GraphVertex.js

@@ -0,0 +1,85 @@
+import LinkedList from '../linked-list/LinkedList';
+
+export default class GraphVertex {
+  constructor(value) {
+    if (value === undefined) {
+      throw new Error('Graph vertex must have a value');
+    }
+
+    // Normally you would store string value like vertex name.
+    // But generally it may be any object as well
+    this.value = value;
+    this.edges = new LinkedList();
+  }
+
+  /**
+   * @param edge {GraphEdge}
+   * @returns {GraphVertex}
+   */
+  addEdge(edge) {
+    this.edges.append(edge);
+
+    return this;
+  }
+
+  getNeighbors() {
+    const edges = this.edges.toArray();
+
+    const neighborsConverter = ({ value }) => {
+      return value.startVertex === this ? value.endVertex : value.startVertex;
+    };
+
+    // Return either start or end vertex.
+    // For undirected graphs it is possible that current vertex will be the end one.
+    return edges.map(neighborsConverter);
+  }
+
+  /**
+   * @param requiredEdge {GraphEdge}
+   * @returns {boolean}
+   */
+  hasEdge(requiredEdge) {
+    const edgeNode = this.edges.find({
+      callback: edge => edge === requiredEdge,
+    });
+
+    return !!edgeNode;
+  }
+
+  /**
+   * @param vertex {GraphVertex}
+   * @returns {boolean}
+   */
+  hasNeighbor(vertex) {
+    const vertexNode = this.edges.find({
+      callback: edge => edge.startVertex === vertex || edge.endVertex === vertex,
+    });
+
+    return !!vertexNode;
+  }
+
+  findEdge(vertex) {
+    const edgeFinder = (edge) => {
+      return edge.startVertex === vertex || edge.endVertex === vertex;
+    };
+
+    const edge = this.edges.find({ callback: edgeFinder });
+
+    return edge ? edge.value : null;
+  }
+
+  /**
+   * @returns {string}
+   */
+  getKey() {
+    return this.value;
+  }
+
+  /**
+   * @param callback {function}
+   * @returns {string}
+   */
+  toString(callback) {
+    return callback ? callback(this.value) : `${this.value}`;
+  }
+}

Diff for: src/data-structures/graph/__test__/Graph.test.js

@@ -0,0 +1,114 @@
+import Graph from '../Graph';
+import GraphVertex from '../GraphVertex';
+import GraphEdge from '../GraphEdge';
+
+describe('Graph', () => {
+  it('should add vertices to graph', () => {
+    const graph = new Graph();
+
+    const vertexA = new GraphVertex('A');
+    const vertexB = new GraphVertex('B');
+
+    graph
+      .addVertex(vertexA)
+      .addVertex(vertexB);
+
+    expect(graph.toString()).toBe('A,B');
+    expect(graph.getVertexByKey(vertexA.getKey())).toEqual(vertexA);
+    expect(graph.getVertexByKey(vertexB.getKey())).toEqual(vertexB);
+  });
+
+  it('should add edges to undirected graph', () => {
+    const graph = new Graph();
+
+    const vertexA = new GraphVertex('A');
+    const vertexB = new GraphVertex('B');
+
+    const edgeAB = new GraphEdge(vertexA, vertexB);
+
+    graph.addEdge(edgeAB);
+
+    const graphVertexA = graph.findVertexByKey(vertexA.getKey());
+    const graphVertexB = graph.findVertexByKey(vertexB.getKey());
+
+    expect(graph.toString()).toBe('A,B');
+    expect(graphVertexA).toBeDefined();
+    expect(graphVertexB).toBeDefined();
+
+    expect(graph.findVertexByKey('not existing')).toBeNull();
+
+    expect(graphVertexA.getNeighbors().length).toBe(1);
+    expect(graphVertexA.getNeighbors()[0]).toEqual(vertexB);
+    expect(graphVertexA.getNeighbors()[0]).toEqual(graphVertexB);
+
+    expect(graphVertexB.getNeighbors().length).toBe(1);
+    expect(graphVertexB.getNeighbors()[0]).toEqual(vertexA);
+    expect(graphVertexB.getNeighbors()[0]).toEqual(graphVertexA);
+  });
+
+  it('should add edges to directed graph', () => {
+    const graph = new Graph(true);
+
+    const vertexA = new GraphVertex('A');
+    const vertexB = new GraphVertex('B');
+
+    const edgeAB = new GraphEdge(vertexA, vertexB);
+
+    graph.addEdge(edgeAB);
+
+    const graphVertexA = graph.findVertexByKey(vertexA.getKey());
+    const graphVertexB = graph.findVertexByKey(vertexB.getKey());
+
+    expect(graph.toString()).toBe('A,B');
+    expect(graphVertexA).toBeDefined();
+    expect(graphVertexB).toBeDefined();
+
+    expect(graphVertexA.getNeighbors().length).toBe(1);
+    expect(graphVertexA.getNeighbors()[0]).toEqual(vertexB);
+    expect(graphVertexA.getNeighbors()[0]).toEqual(graphVertexB);
+
+    expect(graphVertexB.getNeighbors().length).toBe(0);
+  });
+
+  it('should find edge by vertices in undirected graph', () => {
+    const graph = new Graph();
+
+    const vertexA = new GraphVertex('A');
+    const vertexB = new GraphVertex('B');
+    const vertexC = new GraphVertex('C');
+
+    const edgeAB = new GraphEdge(vertexA, vertexB, 10);
+
+    graph.addEdge(edgeAB);
+
+    const graphEdgeAB = graph.findEdge(vertexA, vertexB);
+    const graphEdgeBA = graph.findEdge(vertexB, vertexA);
+    const graphEdgeAC = graph.findEdge(vertexB, vertexC);
+
+    expect(graphEdgeAC).toBeNull();
+    expect(graphEdgeAB).toEqual(edgeAB);
+    expect(graphEdgeBA).toEqual(edgeAB);
+    expect(graphEdgeAB.weight).toBe(10);
+  });
+
+  it('should find edge by vertices in directed graph', () => {
+    const graph = new Graph(true);
+
+    const vertexA = new GraphVertex('A');
+    const vertexB = new GraphVertex('B');
+    const vertexC = new GraphVertex('C');
+
+    const edgeAB = new GraphEdge(vertexA, vertexB, 10);
+
+    graph.addEdge(edgeAB);
+
+    const graphEdgeAB = graph.findEdge(vertexA, vertexB);
+    const graphEdgeBA = graph.findEdge(vertexB, vertexA);
+    const graphEdgeAC = graph.findEdge(vertexB, vertexC);
+
+    expect(graphEdgeAC).toBeNull();
+    expect(graphEdgeBA).toBeNull();
+    expect(graphEdgeAB).toEqual(edgeAB);
+    expect(graphEdgeAB.weight).toBe(10);
+  });
+});

Diff for: src/data-structures/graph/__test__/GraphEdge.test.js

@@ -0,0 +1,24 @@
+import GraphEdge from '../GraphEdge';
+import GraphVertex from '../GraphVertex';
+
+describe('GraphEdge', () => {
+  it('should create graph edge with default weight', () => {
+    const startVertex = new GraphVertex('A');
+    const endVertex = new GraphVertex('B');
+    const edge = new GraphEdge(startVertex, endVertex);
+
+    expect(edge.startVertex).toEqual(startVertex);
+    expect(edge.endVertex).toEqual(endVertex);
+    expect(edge.weight).toEqual(1);
+  });
+
+  it('should create graph edge with predefined weight', () => {
+    const startVertex = new GraphVertex('A');
+    const endVertex = new GraphVertex('B');
+    const edge = new GraphEdge(startVertex, endVertex, 10);
+
+    expect(edge.startVertex).toEqual(startVertex);
+    expect(edge.endVertex).toEqual(endVertex);
+    expect(edge.weight).toEqual(10);
+  });
+});