Added Topological_Sort.js (Fixes jainaman224#2159) (jainaman224#2369)

* Added Topological_Sort.js

* Added Topological_Sort.js

Topological_Sort/Topological_Sort.js

@@ -0,0 +1,92 @@
+// Program to implement Topological Sort
+class Graph {
+    constructor(nodes) {
+        //2 class variables
+        this.nodes = nodes; // no of vertices
+        this.adj = new Array(nodes); // adjacency list
+        for (let i = 0; i < nodes; i++) {
+            this.adj[i] = new Array();
+        }
+        this.stack = []; // a stack for storing the ending times of dfs
+    }
+
+    showGraph = () => {
+        const {
+            nodes,
+            adj
+        } = this; // destructuring for clarity
+
+        for (let i = 0; i < nodes; i++) {
+            // show graph in readable format
+            console.log(`Vertex ${i} is connected to verices `, adj[i]);
+        }
+    };
+
+    addEdge = (x, y) => {
+        const {
+            nodes,
+            adj
+        } = this;
+        // x is connected to y
+        adj[x].push(y);
+    };
+
+    topoSort = () => {
+        const {
+            nodes,
+            adj
+        } = this;
+
+        let visited = new Array(nodes); // visited array
+        for (let i = 0; i < nodes; i++) visited[i] = false;
+
+        for (let i = 0; i < nodes; i++)
+            if (!visited[i]) this.topoUtil(i, visited);
+    };
+
+    topoUtil = (start, visited) => {
+        // utility function of topoSort
+        const {
+            nodes,
+            adj
+        } = this;
+
+        visited[start] = true;
+
+        for (let x of adj[start]) {
+            if (!visited[x]) {
+                this.topoUtil(x, visited);
+            }
+        }
+
+        this.stack.push(start); // push the node when we have completed it
+    };
+}
+
+// implement
+let n = 6; // 6 vertices
+let graph = new Graph(n); // initialise the graph
+
+// add edges
+graph.addEdge(5, 2);
+graph.addEdge(5, 0);
+graph.addEdge(4, 0);
+graph.addEdge(4, 1);
+graph.addEdge(2, 3);
+graph.addEdge(3, 1);
+
+console.log("The Graph is:");
+graph.showGraph();
+
+graph.topoSort();
+console.log(`The Topological sort is `, graph.stack.reverse());
+
+// Output:
+// The Graph is:
+// Vertex 0 is connected to verices  []
+// Vertex 1 is connected to verices  []
+// Vertex 2 is connected to verices  [ 3 ]
+// Vertex 3 is connected to verices  [ 1 ]
+// Vertex 4 is connected to verices  [ 0, 1 ]
+// Vertex 5 is connected to verices  [ 2, 0 ]
+// The topological sort is  [ 5, 4, 2, 3, 1, 0 ]