Tarjan's algo in java

Author: priya-pri

ClassicalAlgos/Tarjan's Algo/TarjanAlgo.java

@@ -0,0 +1,172 @@
+// Java program to find strongly connected components in a given directed graph  using Tarjan's algorithm 
+import java.io.*; 
+import java.util.*; 
+
+
+public class Graph{ 
+private int V;  
+  
+ 
+private LinkedList<Integer> adj[];  
+private int Time; 
+
+Graph(int v) 
+{ 
+	V = v; 
+	adj = new LinkedList[v]; 
+	
+	for(int i = 0; i < v; ++i) 
+		adj[i] = new LinkedList(); 
+		
+	Time = 0; 
+} 
+
+
+void addEdge(int v,int w) 
+{ 
+	adj[v].add(w); 
+} 
+
+			 
+void SCCUtil(int u, int low[], int disc[], 
+			boolean stackMember[], 
+			Stack<Integer> st) 
+{ 
+	
+	
+	disc[u] = Time; 
+	low[u] = Time; 
+	Time += 1; 
+	stackMember[u] = true; 
+	st.push(u); 
+
+	int n; 
+	
+	
+	Iterator<Integer> i = adj[u].iterator(); 
+	
+	while (i.hasNext()) 
+	{ 
+		n = i.next(); 
+		
+		if (disc[n] == -1) 
+		{ 
+			SCCUtil(n, low, disc, stackMember, st); 
+			
+		
+			low[u] = Math.min(low[u], low[n]); 
+		} 
+		else if (stackMember[n] == true) 
+		{ 
+			
+		
+			low[u] = Math.min(low[u], disc[n]); 
+		} 
+	} 
+
+	
+	int w = -1; 
+	if (low[u] == disc[u]) 
+	{ 
+		while (w != u) 
+		{ 
+			w = (int)st.pop(); 
+			System.out.print(w + " "); 
+			stackMember[w] = false; 
+		} 
+		System.out.println(); 
+	} 
+} 
+
+
+void SCC() 
+{ 
+	
+ 
+	int disc[] = new int[V]; 
+	int low[] = new int[V]; 
+	for(int i = 0;i < V; i++) 
+	{ 
+		disc[i] = -1; 
+		low[i] = -1; 
+	} 
+	
+	boolean stackMember[] = new boolean[V]; 
+	Stack<Integer> st = new Stack<Integer>(); 
+	
+	
+	for(int i = 0; i < V; i++) 
+	{ 
+		if (disc[i] == -1) 
+			SCCUtil(i, low, disc, 
+					stackMember, st); 
+	} 
+} 
+
+
+public static void main(String args[]) 
+{ 
+	
+	
+	Graph g1 = new Graph(5); 
+
+	g1.addEdge(1, 0); 
+	g1.addEdge(0, 2); 
+	g1.addEdge(2, 1); 
+	g1.addEdge(0, 3); 
+	g1.addEdge(3, 4); 
+	System.out.println("SSC in first graph "); 
+	g1.SCC(); 
+
+	Graph g2 = new Graph(4); 
+	g2.addEdge(0, 1); 
+	g2.addEdge(1, 2); 
+	g2.addEdge(2, 3); 
+	System.out.println("\nSSC in second graph "); 
+	g2.SCC(); 
+	
+	Graph g3 = new Graph(7); 
+	g3.addEdge(0, 1); 
+	g3.addEdge(1, 2); 
+	g3.addEdge(2, 0); 
+	g3.addEdge(1, 3); 
+	g3.addEdge(1, 4); 
+	g3.addEdge(1, 6); 
+	g3.addEdge(3, 5); 
+	g3.addEdge(4, 5); 
+	System.out.println("\nSSC in third graph "); 
+	g3.SCC(); 
+	
+	Graph g4 = new Graph(11); 
+	g4.addEdge(0, 1); 
+	g4.addEdge(0, 3); 
+	g4.addEdge(1, 2); 
+	g4.addEdge(1, 4); 
+	g4.addEdge(2, 0); 
+	g4.addEdge(2, 6); 
+	g4.addEdge(3, 2); 
+	g4.addEdge(4, 5); 
+	g4.addEdge(4, 6); 
+	g4.addEdge(5, 6); 
+	g4.addEdge(5, 7); 
+	g4.addEdge(5, 8); 
+	g4.addEdge(5, 9); 
+	g4.addEdge(6, 4); 
+	g4.addEdge(7, 9); 
+	g4.addEdge(8, 9); 
+	g4.addEdge(9, 8); 
+	System.out.println("\nSSC in fourth graph "); 
+	g4.SCC(); 
+	
+	Graph g5 = new Graph (5); 
+	g5.addEdge(0, 1); 
+	g5.addEdge(1, 2); 
+	g5.addEdge(2, 3); 
+	g5.addEdge(2, 4); 
+	g5.addEdge(3, 0); 
+	g5.addEdge(4, 2); 
+	System.out.println("\nSSC in fifth graph "); 
+	g5.SCC(); 
+} 
+} 
+