Push Kosaraju's Algorithm in Java

Java/Graphs/Kosaraju_Algorithm.java

@@ -0,0 +1,113 @@
+import java.util.ArrayList;
+import java.util.List;
+
+class GFG {
+
+    // dfs Function to reach destination
+    boolean dfs(int curr, int des, List<List<Integer>> adj,
+                List<Integer> vis) {
+
+        // If curr node is destination return true
+        if (curr == des) {
+            return true;
+        }
+        vis.set(curr, 1);
+        for (int x : adj.get(curr)) {
+            if (vis.get(x) == 0) {
+                if (dfs(x, des, adj, vis)) {
+                    return true;
+                }
+            }
+        }
+        return false;
+    }
+
+    // To tell whether there is path from source to
+    // destination
+    boolean isPath(int src, int des, List<List<Integer>> adj) {
+        List<Integer> vis = new ArrayList<>(adj.size() + 1);
+        for (int i = 0; i <= adj.size(); i++) {
+            vis.add(0);
+        }
+        return dfs(src, des, adj, vis);
+    }
+
+    // Function to return all the strongly connected
+    // component of a graph.
+    List<List<Integer>> findSCC(int n, List<List<Integer>> a) {
+        // Stores all the strongly connected components.
+        List<List<Integer>> ans = new ArrayList<>();
+
+        // Stores whether a vertex is a part of any Strongly
+        // Connected Component
+        List<Integer> is_scc = new ArrayList<>(n + 1);
+        for (int i = 0; i <= n; i++) {
+            is_scc.add(0);
+        }
+
+        List<List<Integer>> adj = new ArrayList<>();
+        for (int i = 0; i <= n; i++) {
+            adj.add(new ArrayList<>());
+        }
+
+        for (List<Integer> edge : a) {
+            adj.get(edge.get(0)).add(edge.get(1));
+        }
+
+        // Traversing all the vertices
+        for (int i = 1; i <= n; i++) {
+
+            if (is_scc.get(i) == 0) {
+
+                // If a vertex i is not a part of any SCC
+                // insert it into a new SCC list and check
+                // for other vertices whether they can be
+                // the part of this list.
+                List<Integer> scc = new ArrayList<>();
+                scc.add(i);
+
+                for (int j = i + 1; j <= n; j++) {
+
+                    // If there is a path from vertex i to
+                    // vertex j and vice versa, put vertex j
+                    // into the current SCC list.
+                    if (is_scc.get(j) == 0 && isPath(i, j, adj)
+                            && isPath(j, i, adj)) {
+                        is_scc.set(j, 1);
+                        scc.add(j);
+                    }
+                }
+
+                // Insert the SCC containing vertex i into
+                // the final list.
+                ans.add(scc);
+            }
+        }
+        return ans;
+    }
+}
+
+public class Main {
+
+    public static void main(String[] args) {
+
+        GFG obj = new GFG();
+        int V = 5;
+        List<List<Integer>> edges = new ArrayList<>();
+        edges.add(new ArrayList<>(List.of(1, 3)));
+        edges.add(new ArrayList<>(List.of(1, 4)));
+        edges.add(new ArrayList<>(List.of(2, 1)));
+        edges.add(new ArrayList<>(List.of(3, 2)));
+        edges.add(new ArrayList<>(List.of(4, 5)));
+        List<List<Integer>> ans = obj.findSCC(V, edges);
+        System.out.println("Strongly Connected Components are:");
+        for (List<Integer> x : ans) {
+            for (int y : x) {
+                System.out.print(y + " ");
+            }
+            System.out.println();
+        }
+    }
+}
+
+// This code is contributed by shivamgupta310570

README.md

@@ -190,7 +190,7 @@
 | 10. | Ford-Fulkerson Algorithm | [C](https://github.com/Kumar-laxmi/Algorithms/blob/main/C/Graphs/FordFulkerson.c), [C++](https://github.com/Kumar-laxmi/Algorithms/blob/main/C%2B%2B/Graphs/Ford-Fulkerson_Algorithm.cpp), [Java](https://github.com/Kumar-laxmi/Algorithms/blob/main/Java/Graphs/FordFulkerson.java), [Python](https://github.com/Kumar-laxmi/Algorithms/blob/main/Python/Graphs/Ford-Fulkerson_Algorithm.py) |
 | 11. | Hamiltonian Path | [Java](https://github.com/Kumar-laxmi/Algorithms/blob/main/Java/Graphs/Hamiltonian_path.java) |
 | 12. | Hopcroft-Karp Algorithm | [C](https://github.com/Kumar-laxmi/Algorithms/blob/main/C/Graphs/Hopcroft-Karp%20algorithm.c), [C++](https://github.com/Kumar-laxmi/Algorithms/blob/main/C%2B%2B/Graphs/Hopcroft-Karp%20algorithm.cpp), [Java](https://github.com/Kumar-laxmi/Algorithms/blob/main/Java/Graphs/Hopcroft-Karp.java), [Python](https://github.com/Kumar-laxmi/Algorithms/blob/main/Python/Graphs/Hopcroft-Karp%20algorithm.py) |
-| 13. | Kosaraju's Algorithm | [C++](https://github.com/Kumar-laxmi/Algorithms/blob/main/C%2B%2B/Graphs/Kosaraju_Algorithm.cpp) |
+| 13. | Kosaraju's Algorithm | [C++](https://github.com/Kumar-laxmi/Algorithms/blob/main/C%2B%2B/Graphs/Kosaraju_Algorithm.cpp), [Java](https://github.com/Kumar-laxmi/Algorithms/blob/main/Java/Graphs/Kosaraju_Algorithm.java) |
 | 14. | Kruskal's Algorithm | [C](https://github.com/Kumar-laxmi/Algorithms/blob/main/C/Graphs/Kruskals.c), [C++](https://github.com/Kumar-laxmi/Algorithms/blob/main/C%2B%2B/Graphs/Kruskals.cpp), [Java](https://github.com/Kumar-laxmi/Algorithms/blob/main/Java/Graphs/Kruskals.java), [Python](https://github.com/Kumar-laxmi/Algorithms/blob/main/Python/Graphs/Kruskals.py) |
 | 15. | Multi Source Shortest Path | [C](https://github.com/Kumar-laxmi/Algorithms/blob/main/C/Graphs/Multisource_Shortest_Path.c), [C++](https://github.com/Kumar-laxmi/Algorithms/blob/main/C%2B%2B/Graphs/Multisource_Shortest_Path.cpp), [Java](https://github.com/Kumar-laxmi/Algorithms/blob/main/Java/Graphs/Multisource_Shortest_Path.java), [Python](https://github.com/Kumar-laxmi/Algorithms/blob/main/Python/Graphs/MultiSource_Shortest_Path.py) |
 | 16. | Multistage Graph (Shortest Path) | [C](https://github.com/Kumar-laxmi/Algorithms/blob/main/C/Graphs/multistage_graph.c), [C++](https://github.com/Kumar-laxmi/Algorithms/blob/main/C%2B%2B/Graphs/multistage_graph.cpp), [Java](https://github.com/Kumar-laxmi/Algorithms/blob/main/Java/Graphs/MultistageGraph.java), [Python](https://github.com/Kumar-laxmi/Algorithms/blob/main/Python/Graphs/multistage_graph.py) |