Patch 1

README.md

@@ -1 +1,2 @@
 # Algorithms
+this is an algorithm

breadthFirstSearch.js

@@ -0,0 +1,55 @@
+import Queue from '../../../data-structures/queue/Queue';
+
+function initCallbacks(callbacks = {}) {
+  const initiatedCallback = callbacks;
+
+  const stubCallback = () => {};
+
+  const allowTraversalCallback = (
+    () => {
+      const seen = {};
+      return ({ nextVertex }) => {
+        if (!seen[nextVertex.getKey()]) {
+          seen[nextVertex.getKey()] = true;
+          return true;
+        }
+        return false;
+      };
+    }
+  )();
+
+  initiatedCallback.allowTraversal = callbacks.allowTraversal || allowTraversalCallback;
+  initiatedCallback.enterVertex = callbacks.enterVertex || stubCallback;
+  initiatedCallback.leaveVertex = callbacks.leaveVertex || stubCallback;
+
+  return initiatedCallback;
+}
+
+
+export default function breadthFirstSearch(graph, startVertex, originalCallbacks) {
+  const callbacks = initCallbacks(originalCallbacks);
+  const vertexQueue = new Queue();
+
+  // Do initial queue setup.
+  vertexQueue.enqueue(startVertex);
+
+  let previousVertex = null;
+
+  // Traverse all vertices from the queue.
+  while (!vertexQueue.isEmpty()) {
+    const currentVertex = vertexQueue.dequeue();
+    callbacks.enterVertex({ currentVertex, previousVertex });
+
+    // Add all neighbors to the queue for future traversals.
+    graph.getNeighbors(currentVertex).forEach((nextVertex) => {
+      if (callbacks.allowTraversal({ previousVertex, currentVertex, nextVertex })) {
+        vertexQueue.enqueue(nextVertex);
+      }
+    });
+
+    callbacks.leaveVertex({ currentVertex, previousVertex });
+
+    // Memorize current vertex before next loop.
+    previousVertex = currentVertex;
+  }
+}