Add graph.

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();
+  }
+}