169 lines
5.8 KiB
Java
169 lines
5.8 KiB
Java
import java.util.HashMap;
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import java.util.InputMismatchException;
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import java.util.Map;
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import java.util.Scanner;
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import java.util.Stack;
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public class StrongConnectedComponents
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{
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private int leader = 0;
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private int[] leader_node;
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private int explore[];
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private int finishing_time_of_node[];
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private int finishing_time = 1;
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private int number_of_nodes;
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private Stack<Integer> stack;
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private Map<Integer, Integer> finishing_time_map;
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public StrongConnectedComponents(int number_of_nodes)
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{
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this.number_of_nodes = number_of_nodes;
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leader_node = new int[number_of_nodes + 1];
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explore = new int[number_of_nodes + 1];
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finishing_time_of_node = new int[number_of_nodes + 1];
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stack = new Stack<Integer>();
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finishing_time_map = new HashMap<Integer, Integer>();
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}
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public void strongConnectedComponent(int adjacency_matrix[][])
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{
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for (int i = number_of_nodes; i > 0; i--)
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{
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if (explore[i] == 0)
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{
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dfs_1(adjacency_matrix, i);
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}
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}
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int rev_matrix[][] = new int[number_of_nodes + 1][number_of_nodes + 1];
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for (int i = 1; i <= number_of_nodes; i++)
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{
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for (int j = 1; j <= number_of_nodes; j++)
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{
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if (adjacency_matrix[i][j] == 1)
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rev_matrix[finishing_time_of_node[j]][finishing_time_of_node[i]] = adjacency_matrix[i][j];
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}
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}
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for (int i = 1; i <= number_of_nodes; i++)
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{
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explore[i] = 0;
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leader_node[i] = 0;
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}
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for (int i = number_of_nodes; i > 0; i--)
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{
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if (explore[i] == 0)
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{
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leader = i;
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dfs_2(rev_matrix, i);
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}
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}
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}
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public void dfs_1(int adjacency_matrix[][], int source)
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{
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explore[source] = 1;
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stack.push(source);
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int i = 1;
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int element = source;
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while (!stack.isEmpty())
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{
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element = stack.peek();
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i = 1;
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while (i <= number_of_nodes)
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{
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if (adjacency_matrix[element][i] == 1 && explore[i] == 0)
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{
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stack.push(i);
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explore[i] = 1;
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element = i;
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i = 1;
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continue;
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}
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i++;
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}
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int poped = stack.pop();
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int time = finishing_time++;
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finishing_time_of_node[poped] = time;
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finishing_time_map.put(time, poped);
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}
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}
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public void dfs_2(int rev_matrix[][], int source)
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{
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explore[source] = 1;
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leader_node[finishing_time_map.get(source)] = leader;
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stack.push(source);
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int i = 1;
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int element = source;
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while (!stack.isEmpty())
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{
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element = stack.peek();
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i = 1;
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while (i <= number_of_nodes)
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{
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if (rev_matrix[element][i] == 1 && explore[i] == 0)
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{
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if (leader_node[finishing_time_map.get(i)] == 0)
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leader_node[finishing_time_map.get(i)] = leader;
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stack.push(i);
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explore[i] = 1;
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element = i;
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i = 1;
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continue;
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}
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i++;
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}
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stack.pop();
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}
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}
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public static void main(String... arg)
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{
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int number_of_nodes;
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Scanner scanner = null;
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try
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{
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System.out.println("Enter the number of nodes in the graph");
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scanner = new Scanner(System.in);
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number_of_nodes = scanner.nextInt();
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int adjacency_matrix[][] = new int[number_of_nodes + 1][number_of_nodes + 1];
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System.out.println("Enter the adjacency matrix");
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for (int i = 1; i <= number_of_nodes; i++)
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for (int j = 1; j <= number_of_nodes; j++)
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adjacency_matrix[i][j] = scanner.nextInt();
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StrongConnectedComponents strong = new StrongConnectedComponents(number_of_nodes);
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strong.strongConnectedComponent(adjacency_matrix);
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System.out.println("The Strong Connected Components are");
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for (int i = 1; i < strong.leader_node.length; i++)
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{
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System.out.println( "Node " + i+ "belongs to SCC"
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+ strong.finishing_time_map.get(strong.leader_node[i]));
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}
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}
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catch (InputMismatchException inputMismatch)
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{
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System.out.println("Wrong Input Format");
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}
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}
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}
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/*
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Enter the number of nodes in the graph
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8
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Enter the adjacency matrix
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0 1 0 0 0 0 0 0
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0 0 0 0 0 0 1 0
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0 0 0 1 1 0 0 0
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0 1 0 0 0 0 1 0
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0 0 0 0 0 0 0 1
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1 1 0 0 0 0 0 0
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0 0 0 0 0 1 0 0
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0 0 1 1 0 0 0 0
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The Strong Connected Components are
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Node 1 belongs to SCC 2
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Node 2 belongs to SCC 2
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Node 3 belongs to SCC 8
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Node 4 belongs to SCC 4
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Node 5 belongs to SCC 8
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Node 6 belongs to SCC 2
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Node 7 belongs to SCC 2
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Node 8 belongs to SCC 8 |