From cb0aff9ec2fe6503fb79b7069c2dc37d6e2509f2 Mon Sep 17 00:00:00 2001
From: Sahil <shlbnsl843@gmail.com>
Date: Mon, 18 May 2020 10:15:53 +0530
Subject: [PATCH] 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>
---
 Data-Structures/Graph/Graph.js | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/Data-Structures/Graph/Graph.js b/Data-Structures/Graph/Graph.js
index ef1a952a8..503d9b498 100644
--- a/Data-Structures/Graph/Graph.js
+++ b/Data-Structures/Graph/Graph.js
@@ -30,6 +30,31 @@ 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 = () => {
@@ -37,8 +62,17 @@ const example = () => {
   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()