Add Topological Sort algorithm using DFS in GraphSearch

Author: Saipatnaik-23

src/main/java/com/thealgorithms/graphsearch/TopologicalSort.java

@@ -0,0 +1,83 @@
+package com.thealgorithms.graphsearch;
+
+import java.util.ArrayList;
+import java.util.Stack;
+
+/**
+ * This class implements the Topological Sort algorithm using Depth-First Search
+ * for Directed Acyclic Graphs. It prints the nodes in a topological order.
+ */
+
+public class TopologicalSort {
+    /**
+     * Main method to test the Topological Sort implementation.
+     * Creates a sample graph and prints its topological ordering.
+     * @param args command-line arguments(not used)
+     */
+
+    public static void main(String[] args) {
+        int v = 6;
+        ArrayList<ArrayList<Integer>> adjList = new ArrayList<>();
+        for(int i=0; i<v; i++){
+            adjList.add(new ArrayList<>());
+        }
+
+        //sample DAG edges
+        adjList.get(5).add(2);
+        adjList.get(5).add(0);
+        adjList.get(4).add(0);
+        adjList.get(4).add(1);
+        adjList.get(2).add(3);
+        adjList.get(3).add(1);
+
+        topoSort(v,adjList);
+    }
+
+    /**
+     * Performs the topological sort on the given graph represented by adjacency list.
+     * Prints the nodes in topologically sorted order.
+     *
+     * @param v  the number of vertices in the graph
+     * @param adjList adjacency list representing the graph
+     */
+
+
+    public static void topoSort (int v, ArrayList<ArrayList<Integer>> adjList){
+        boolean []  visited = new boolean[v];
+        Stack <Integer> stack = new Stack<>();
+
+        for (int i = 0; i < v; i++) {
+            if(!visited[i]){
+                topoSortUtil(i,visited,stack,adjList);
+            }
+        }
+
+        System.out.println("Topological Sort:");
+        while (!stack.isEmpty()){
+            System.out.print(stack.pop()+" ");
+        }
+        System.out.println();
+    }
+
+    /**
+     *  Utility method to perform DFS starting from a given node.
+     *  Marks nodes as visited and pushes nodes to stack after visiting all their neighbors.
+     *
+     * @param node the current node being visited
+     * @param visited boolean array tracking visited nodes
+     * @param stack stack to store the topological order
+     * @param adjList adjacency list representing the graph
+     *
+     */
+
+    public static void topoSortUtil(int node, boolean[] visited, Stack<Integer> stack, ArrayList<ArrayList<Integer>> adjList){
+        visited[node] = true;
+
+        for(int neighbour : adjList.get(node)){
+            if(!visited[neighbour]){
+                topoSortUtil(neighbour,visited,stack,adjList);
+            }
+        }
+        stack.push(node); // add to stack after visiting all edges
+    }
+}