Add Graph BFS algorithm (#169)

* Add Graph BFS algorithm

* updating DIRECTORY.md

* Fix failing tests

* updating DIRECTORY.md

* Fix further failing tests

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>

Author: sahilbansal17

Data-Structures/Graph/Graph.js

@@ -30,15 +30,49 @@ class Graph {
       console.log(i + ' -> ' + vertex)
     }
   }
+
+  /**
+   * Prints the Breadth first traversal of the graph from source.
+   *
+   * @param {number} source The source vertex to start BFS.
+   */
+  bfs (source) {
+    const queue = []
+    const visited = new Set()
+    queue.unshift([source, 0]) // level of source is 0
+    visited.add(source)
+    while (queue.length) {
+      const front = queue[0]
+      const node = front[0]
+      const level = front[1]
+      queue.shift() // remove the front of the queue
+      console.log(`Visited node ${node} at level ${level}.`)
+      for (const next of this.adjacencyMap[node]) {
+        if (!visited.has(next)) { // not visited
+          queue.unshift([next, level + 1]) // level 1 more than current
+          visited.add(next)
+        }
+      }
+    }
+  }
 }
 
 const example = () => {
   const g = new Graph()
   g.addVertex(1)
   g.addVertex(2)
   g.addVertex(3)
+  g.addVertex(4)
+  g.addVertex(5)
   g.addEdge(1, 2)
   g.addEdge(1, 3)
+  g.addEdge(2, 4)
+  g.addEdge(2, 5)
+  console.log('Printing the adjacency list:\n')
   g.printGraph()
+
+  // perform a breadth first search
+  console.log('\nBreadth first search at node 1:\n')
+  g.bfs(1)
 }
 example()