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TopologicalSortingDFS.java

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+package Graph;
+
+import java.util.ArrayList;
+import java.util.Scanner;
+import java.util.Stack;
+
+public class TopologicalSortingDFS {
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        ArrayList<ArrayList<Integer>> adjacencyList = new ArrayList<>();
+
+        // Taking input for number of nodes
+        System.out.println("Enter the number of nodes:");
+        int numberOfNodes = sc.nextInt();
+
+        // initializing adjacencyList with new ArrayList<>()
+        for(int i=1 ; i<=numberOfNodes+1 ; i++){
+            adjacencyList.add(new ArrayList<>());
+        }
+
+        // taking input of adjacent nodes of particular node
+        for(int i=1 ; i<=numberOfNodes ; i++){
+            System.out.println("Enter number of adjacent nodes to the node : " + i);
+            int countOfAdjacentNodes = sc.nextInt();
+
+            // taking input of the particular adjacent nodes to the node i
+            System.out.println("Enter adjacent nodes:");
+            for(int j=0 ; j<countOfAdjacentNodes ; j++){
+
+                // taking input of adjacent node
+                int adjacentNode = sc.nextInt();
+                // adding the adjacent node to the particular node i
+                adjacencyList.get(i).add(adjacentNode);
+            }
+        }
+
+        // This is a helper method which is used to call to topologicalSort method
+        // for printing the topological sort of the given graph
+        helperMethod(adjacencyList, numberOfNodes);
+    }
+    public static void helperMethod(ArrayList<ArrayList<Integer>> adjacencyList, int numberOfNodes){
+        boolean[] visitedNodes = new boolean[numberOfNodes+1];  // visited array
+        Stack<Integer> stack = new Stack<>();   // Stack data structure for storing topological sorting
+
+        // Run loop for all nodes
+        for(int node=1 ; node<=numberOfNodes ; node++){
+            // If not visited then call for topologicalSort method
+            if(!visitedNodes[node]){
+                topologicalSort(node, adjacencyList, visitedNodes, stack);
+            }
+        }
+
+        // Topological sorting of the given graph is printed here
+        System.out.println("Topological sorting of the given graph is :");
+        while(!stack.isEmpty()){
+            System.out.print(stack.pop() + " ");
+        }
+    }
+    public static void topologicalSort(int node, ArrayList<ArrayList<Integer>> adjacencyList, boolean[] visitedNodes, Stack<Integer> stack){
+        visitedNodes[node] = true;  // mark the current node visited
+
+        // now check for all adjacent nodes of the current node
+        for(int adjacentNode : adjacencyList.get(node)){
+            // if not visited then call method
+            if(!visitedNodes[adjacentNode]){
+                topologicalSort(adjacentNode, adjacencyList, visitedNodes, stack);
+            }
+        }
+        stack.add(node);    // at last add the current node into the stack data structure
+    }
+}