123 lines
3.6 KiB
Java
123 lines
3.6 KiB
Java
/*This is a java program to check whether a graph is strongly connected or weakly connected. If graph has more than one connected components it is weakly connected. If graph has only one connected component it is strongly connected.*/
|
|
|
|
|
|
import java.util.ArrayList;
|
|
import java.util.Iterator;
|
|
import java.util.List;
|
|
import java.util.Scanner;
|
|
import java.util.Stack;
|
|
|
|
public class StronglyorWeaklyConnectedDigraphs
|
|
{
|
|
private int V;
|
|
private int preCount;
|
|
private int[] low;
|
|
private boolean[] visited;
|
|
private List<Integer>[] graph;
|
|
private List<List<Integer>> sccComp;
|
|
private Stack<Integer> stack;
|
|
|
|
/** function to get all strongly connected components **/
|
|
public List<List<Integer>> getSCComponents(List<Integer>[] graph)
|
|
{
|
|
V = graph.length;
|
|
this.graph = graph;
|
|
low = new int[V];
|
|
visited = new boolean[V];
|
|
stack = new Stack<Integer>();
|
|
sccComp = new ArrayList<>();
|
|
for (int v = 0; v < V; v++)
|
|
if (!visited[v])
|
|
dfs(v);
|
|
return sccComp;
|
|
}
|
|
|
|
/** function dfs **/
|
|
public void dfs(int v)
|
|
{
|
|
low[v] = preCount++;
|
|
visited[v] = true;
|
|
stack.push(v);
|
|
int min = low[v];
|
|
for (int w : graph[v])
|
|
{
|
|
if (!visited[w])
|
|
dfs(w);
|
|
if (low[w] < min)
|
|
min = low[w];
|
|
}
|
|
if (min < low[v])
|
|
{
|
|
low[v] = min;
|
|
return;
|
|
}
|
|
List<Integer> component = new ArrayList<Integer>();
|
|
int w;
|
|
do
|
|
{
|
|
w = stack.pop();
|
|
component.add(w);
|
|
low[w] = V;
|
|
}
|
|
while (w != v);
|
|
sccComp.add(component);
|
|
}
|
|
|
|
@SuppressWarnings("unchecked")
|
|
public static void main(String[] args)
|
|
{
|
|
Scanner scan = new Scanner(System.in);
|
|
System.out.println("Enter number of Vertices");
|
|
/** number of vertices **/
|
|
int V = scan.nextInt();
|
|
/** make graph **/
|
|
List<Integer>[] g = new List[V];
|
|
for (int i = 0; i < V; i++)
|
|
g[i] = new ArrayList<Integer>();
|
|
/** accept all edges **/
|
|
System.out.println("Enter number of edges");
|
|
int E = scan.nextInt();
|
|
/** all edges **/
|
|
System.out.println("Enter the edges in the graph : <from> <to>");
|
|
for (int i = 0; i < E; i++)
|
|
{
|
|
int x = scan.nextInt();
|
|
int y = scan.nextInt();
|
|
g[x].add(y);
|
|
}
|
|
StronglyConnectedGraph t = new StronglyConnectedGraph();
|
|
System.out.print("The graph is : ");
|
|
/** print all strongly connected components **/
|
|
List<List<Integer>> scComponents = t.getSCComponents(g);
|
|
Iterator<List<Integer>> iterator = scComponents.iterator();
|
|
boolean weaklyConnected = false;
|
|
while (iterator.hasNext())
|
|
{
|
|
if (iterator.next().size() <= 1)
|
|
{
|
|
weaklyConnected = true;
|
|
}
|
|
}
|
|
if (weaklyConnected == true)
|
|
System.out.println("Weakly Connected");
|
|
else
|
|
System.out.println("Strongly Connected");
|
|
scan.close();
|
|
}
|
|
}
|
|
|
|
/*
|
|
Enter number of Vertices
|
|
|
|
6
|
|
Enter number of edges
|
|
7
|
|
Enter the edges in the graph : <from> <to>
|
|
0 1
|
|
1 2
|
|
1 3
|
|
3 4
|
|
4 5
|
|
5 3
|
|
5 2
|
|
The graph is : Weakly Connected |