This Java program, displays the Strong Connected Components of graph.A directed graph is called strongly connected if there is a path from each vertex in the graph to every other vertex. In particular , this means paths in each direction; a path from a to b and also a path from b to a.

Here is the source code of the Java program to display the Strong Connected Components of a graph. The Java program is successfully compiled and run on a Linux system. The program output is also shown below.

import java.util.HashMap;

import java.util.InputMismatchException;

import java.util.Map;

import java.util.Scanner;

import java.util.Stack;

public class StrongConnectedComponents

`{`

private int leader = 0;

private int[] leader_node;

private int explore[];

private int finishing_time_of_node[];

private int finishing_time = 1;

private int number_of_nodes;

private Stack<Integer> stack;

private Map<Integer, Integer> finishing_time_map;

public StrongConnectedComponents(int number_of_nodes)

`{`

this.number_of_nodes = number_of_nodes;

leader_node = new int[number_of_nodes + 1];

explore = new int[number_of_nodes + 1];

finishing_time_of_node = new int[number_of_nodes + 1];

stack = new Stack<Integer>();

finishing_time_map = new HashMap<Integer, Integer>();

`}`

public void strongConnectedComponent(int adjacency_matrix[][])

`{`

for (int i = number_of_nodes; i > 0; i--)

`{`

if (explore[i] == 0)

`{`

dfs_1(adjacency_matrix, i);

`}`

`}`

int rev_matrix[][] = new int[number_of_nodes + 1][number_of_nodes + 1];

for (int i = 1; i <= number_of_nodes; i++)

`{`

for (int j = 1; j <= number_of_nodes; j++)

`{`

if (adjacency_matrix[i][j] == 1)

rev_matrix[finishing_time_of_node[j]][finishing_time_of_node[i]] = adjacency_matrix[i][j];

`}`

`}`

for (int i = 1; i <= number_of_nodes; i++)

`{`

explore[i] = 0;

leader_node[i] = 0;

`}`

for (int i = number_of_nodes; i > 0; i--)

`{`

if (explore[i] == 0)

`{`

leader = i;

dfs_2(rev_matrix, i);

`}`

`}`

`}`

public void dfs_1(int adjacency_matrix[][], int source)

`{`

explore[source] = 1;

stack.push(source);

int i = 1;

int element = source;

while (!stack.isEmpty())

`{`

element = stack.peek();

i = 1;

while (i <= number_of_nodes)

`{`

if (adjacency_matrix[element][i] == 1 && explore[i] == 0)

`{`

stack.push(i);

explore[i] = 1;

element = i;

i = 1;

continue;

`}`

`i++;`

`}`

int poped = stack.pop();

int time = finishing_time++;

finishing_time_of_node[poped] = time;

finishing_time_map.put(time, poped);

`}`

`}`

public void dfs_2(int rev_matrix[][], int source)

`{`

explore[source] = 1;

leader_node[finishing_time_map.get(source)] = leader;

stack.push(source);

int i = 1;

int element = source;

while (!stack.isEmpty())

`{`

element = stack.peek();

i = 1;

while (i <= number_of_nodes)

`{`

if (rev_matrix[element][i] == 1 && explore[i] == 0)

`{`

if (leader_node[finishing_time_map.get(i)] == 0)

leader_node[finishing_time_map.get(i)] = leader;

stack.push(i);

explore[i] = 1;

element = i;

i = 1;

continue;

`}`

`i++;`

`}`

stack.pop();

`}`

`}`

public static void main(String... arg)

`{`

int number_of_nodes;

Scanner scanner = null;

`try`

`{`

System.out.println("Enter the number of nodes in the graph");

scanner = new Scanner(System.in);

number_of_nodes = scanner.nextInt();

int adjacency_matrix[][] = new int[number_of_nodes + 1][number_of_nodes + 1];

System.out.println("Enter the adjacency matrix");

for (int i = 1; i <= number_of_nodes; i++)

for (int j = 1; j <= number_of_nodes; j++)

adjacency_matrix[i][j] = scanner.nextInt();

StrongConnectedComponents strong = new StrongConnectedComponents(number_of_nodes);

strong.strongConnectedComponent(adjacency_matrix);

System.out.println("The Strong Connected Components are");

for (int i = 1; i < strong.leader_node.length; i++)

`{`

System.out.println( "Node " + i+ "belongs to SCC"

+ strong.finishing_time_map.get(strong.leader_node[i]));

`}`

} catch (InputMismatchException inputMismatch)

`{`

System.out.println("Wrong Input Format");

`}`

`}`

`}`

$javac StrongConnectedComponents.java $java StrongConnectedComponenets Enter the number of nodes in the graph 8 Enter the adjacency matrix 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 1 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 1 0 0 0 0 The Strong Connected Components are Node 1 belongs to SCC 2 Node 2 belongs to SCC 2 Node 3 belongs to SCC 8 Node 4 belongs to SCC 4 Node 5 belongs to SCC 8 Node 6 belongs to SCC 2 Node 7 belongs to SCC 2 Node 8 belongs to SCC 8

**Sanfoundry Global Education & Learning Series – 1000 Java Programs.**

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