Added Tarjan’s Algorithm in Java

Algorithms/TarjanSCC.java

@@ -0,0 +1,85 @@
+// Tarjan’s Algorithm in Java
+// ------------------------------------------------------
+// Author: Jatin Vishwakarma
+// Description: Implementation of Tarjan’s Algorithm for finding
+// Strongly Connected Components (SCCs) in a directed graph.
+// This algorithm uses DFS and low-link values to efficiently
+// detect all SCCs in O(V + E) time complexity.
+
+import java.util.*;
+
+public class TarjanSCC {
+    private final int V; 
+    private final List<List<Integer>> adj; 
+    private int time; 
+    private final int[] disc; 
+    private final int[] low; 
+    private final boolean[] stackMember; 
+    private final Stack<Integer> stack; 
+
+    public TarjanSCC(int vertices) {
+        V = vertices;
+        adj = new ArrayList<>();
+        for (int i = 0; i < vertices; i++) adj.add(new ArrayList<>());
+        disc = new int[vertices];
+        low = new int[vertices];
+        stackMember = new boolean[vertices];
+        stack = new Stack<>();
+        Arrays.fill(disc, -1); 
+        Arrays.fill(low, -1);
+    }
+
+    // Add a directed edge from u to v
+    public void addEdge(int u, int v) {
+        adj.get(u).add(v);
+    }
+
+    private void SCCUtil(int u) {
+        disc[u] = low[u] = ++time;
+        stack.push(u);
+        stackMember[u] = true;
+
+        for (int v : adj.get(u)) {
+            if (disc[v] == -1) { // If v is not visited
+                SCCUtil(v);
+                low[u] = Math.min(low[u], low[v]);
+            } else if (stackMember[v]) { // Back edge
+                low[u] = Math.min(low[u], disc[v]);
+            }
+        }
+
+        // If u is the root of an SCC
+        if (low[u] == disc[u]) {
+            System.out.print("SCC: ");
+            while (true) {
+                int v = stack.pop();
+                stackMember[v] = false;
+                System.out.print(v + " ");
+                if (v == u) break;
+            }
+            System.out.println();
+        }
+    }
+
+    public void findSCCs() {
+        for (int i = 0; i < V; i++) {
+            if (disc[i] == -1)
+                SCCUtil(i);
+        }
+    }
+
+    public static void main(String[] args) {
+        TarjanSCC g = new TarjanSCC(7);
+        g.addEdge(0, 1);
+        g.addEdge(1, 2);
+        g.addEdge(2, 0);
+        g.addEdge(1, 3);
+        g.addEdge(3, 4);
+        g.addEdge(4, 5);
+        g.addEdge(5, 3);
+        g.addEdge(5, 6);
+
+        System.out.println("Strongly Connected Components in the given graph:");
+        g.findSCCs();
+    }
+}