Added DFS Traversal in Java

Java/algorithms/graph_algorithms/DFSTraversal.java

@@ -0,0 +1,84 @@
+/* Algorithm Name
+DFS (Depth First Search Traversal)
+
+Programming Language
+Java
+
+Category
+Traversing / Searching
+
+Difficulty Level
+Easy
+
+* Algorithm Description : 
+
+1. Problem it solves:
+
+-> Used for graph traversal and can be applied for topological sorting, cycle detection, and pathfinding problems.
+
+2. Approach / Idea:
+-> DFS uses a stack (can be implemented recursively or iteratively) and explores nodes as deep as possible before backtracking.
+
+-> Start from the source node and mark it as visited.
+
+-> Visit all unvisited neighbors recursively (or using a stack).
+
+-> Continue until all reachable nodes are visited.
+
+3. Complexity:
+
+Time: O(V + E), where V = number of vertices and E = number of edges.
+Space: O(V) for the recursion stack or explicit stack and visited set/array.
+
+* Author : Subhodeep Chatterjee
+
+*/
+
+import java.util.*;
+
+public class DFSTraversal {
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        // Input vertices and edges
+        System.out.print("Enter number of vertices: ");
+        int V = sc.nextInt();
+        System.out.print("Enter number of edges: ");
+        int E = sc.nextInt();
+
+        // Graph as adjacency list
+        Map<Integer, List<Integer>> graph = new HashMap<>();
+
+        System.out.println("Enter edges (u v): ");
+        for (int i = 0; i < E; i++) {
+            int u = sc.nextInt();
+            int v = sc.nextInt();
+            addEdge(graph, u, v); // undirected edge
+        }
+
+        System.out.print("Enter starting node: ");
+        int start = sc.nextInt();
+
+        System.out.println("DFS Traversal:");
+        Set<Integer> visited = new HashSet<>();
+        dfs(graph, start, visited);
+    }
+
+    // Function to add edge (undirected graph)
+    static void addEdge(Map<Integer, List<Integer>> graph, int u, int v) {
+        graph.computeIfAbsent(u, k -> new ArrayList<>()).add(v);
+        // avoid the given below line if you want directed graph
+        graph.computeIfAbsent(v, k -> new ArrayList<>()).add(u);
+    }
+
+    // Recursive DFS Function
+    static void dfs(Map<Integer, List<Integer>> graph, int node, Set<Integer> visited) {
+        visited.add(node);
+        System.out.print(node + " ");
+
+        for (int neighbour : graph.getOrDefault(node, new ArrayList<>())) {
+            if (!visited.contains(neighbour)) {
+                dfs(graph, neighbour, visited);
+            }
+        }
+    }
+}