Added TopologicalSort implementaion on graph.

Data-Structures/Graph/Graph.js

@@ -1,14 +1,16 @@
 class Graph {
   constructor () {
     this.adjacencyMap = {}
+    this.numberOfVertex = 0
   }
 
   addVertex (vertex) {
     this.adjacencyMap[vertex] = []
+    this.numberOfVertex++
   }
 
   containsVertex (vertex) {
-    return typeof (this.adjacencyMap[vertex]) !== 'undefined'
+    return typeof this.adjacencyMap[vertex] !== 'undefined'
   }
 
   addEdge (vertex1, vertex2) {
@@ -18,7 +20,7 @@ class Graph {
     }
   }
 
-  printGraph (output = value => console.log(value)) {
+  printGraph (output = (value) => console.log(value)) {
     const keys = Object.keys(this.adjacencyMap)
     for (const i of keys) {
       const values = this.adjacencyMap[i]
@@ -34,13 +36,14 @@ class Graph {
    * Prints the Breadth first traversal of the graph from source.
    * @param {number} source The source vertex to start BFS.
    */
-  bfs (source, output = value => console.log(value)) {
+  bfs (source, output = (value) => console.log(value)) {
     const queue = [[source, 0]] // level of source is 0
     const visited = new Set()
 
     while (queue.length) {
       const [node, level] = queue.shift() // remove the front of the queue
-      if (visited.has(node)) { // visited
+      if (visited.has(node)) {
+        // visited
         continue
       }
 
@@ -56,8 +59,9 @@ class Graph {
    * Prints the Depth first traversal of the graph from source.
    * @param {number} source The source vertex to start DFS.
    */
-  dfs (source, visited = new Set(), output = value => console.log(value)) {
-    if (visited.has(source)) { // visited
+  dfs (source, visited = new Set(), output = (value) => console.log(value)) {
+    if (visited.has(source)) {
+      // visited
       return
     }
 
@@ -67,6 +71,40 @@ class Graph {
       this.dfs(neighbour, visited, output)
     }
   }
+
+  _topologicalSort (v, visited, stack) {
+    // Mark the current node as visited.
+    visited[v] = true
+
+    // Recur for all the vertices adjacent to thisvertex
+    for (const i of this.adjacencyMap[v]) {
+      if (!visited[i]) {
+        this._topologicalSort(i, visited, stack)
+      }
+    }
+
+    // Push current vertex to stack which stores result
+    stack.push(v)
+  }
+
+  // The function to do Topological Sort. It uses recursive _topologicalSort()
+  topologicalSort () {
+    const stack = []
+
+    // Mark all the vertices as not visited
+    const visited = new Array(this.numberOfVertex)
+    visited.fill(false)
+
+    // Call the recursive helper function to store Topological Sort starting from all vertices one by one
+    for (let i = 0; i < visited.length; i++) {
+      if (visited[i] === false) {
+        this._topologicalSort(i + 1, visited, stack)
+      }
+    }
+
+    // Return stack in reverse order
+    return stack.reverse()
+  }
 }
 
 const example = () => {
@@ -96,6 +134,9 @@ const example = () => {
 
   // Depth first search at node 1
   g.dfs(1)
+
+  // Prints Topological sort of given graph
+  g.topologicalSort()
 }
 
 export { Graph, example }