Add graph.

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}`;
+  }
+}