Java Program to Detect Cycle in a Graph using Graph Traversal

This Java program,performs the DFS traversal on the given graph represented by a adjacency matrix to check for cycles in the graph.the DFS traversal makes use of an stack.

Here is the source code of the Java program to check for cycle in graph.The Java program is successfully compiled and run on a Linux system. The program output is also shown below.

import java.util.InputMismatchException;

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import java.util.Scanner;
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import java.util.Stack;
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```
```
public class CheckCycle
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```
{
```
```
    private Stack<Integer> stack;
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```
    private int adjacencyMatrix[][];
```
```
 
```
```
    public CheckCycle() 
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    {
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        stack = new Stack<Integer>();
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    }
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```
 
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    public void dfs(int adjacency_matrix[][], int source)

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    {
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        int number_of_nodes = adjacency_matrix[source].length - 1;

```
 
```

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

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

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        {
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            for (int destinationvertex = 1; destinationvertex <= number_of_nodes; destinationvertex++)

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            {
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                adjacencyMatrix[sourcevertex][destinationvertex] =

                   adjacency_matrix[sourcevertex][destinationvertex];

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            }
```
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        }
```
```
 
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        int visited[] = new int[number_of_nodes + 1];

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        int element = source;		
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        int destination = source;			
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        visited[source] = 1;		
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        stack.push(source);
```
```
 
```
```
        while (!stack.isEmpty())
```
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        {
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            element = stack.peek();
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            destination = element;	
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	    while (destination <= number_of_nodes)

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	    {
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                if (adjacencyMatrix[element][destination] == 1 && visited[destination] == 1)

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                {
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                    if (stack.contains(destination))

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                    {	
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                        System.out.println("The Graph contains cycle");

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                        return;	
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                    }
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                }
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              	if (adjacencyMatrix[element][destination] == 1 && visited[destination] == 0)

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	        {
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                    stack.push(destination);

                    visited[destination] = 1;

                    adjacencyMatrix[element][destination] = 0;

                    element = destination;

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                    destination = 1;
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	            continue;
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                }
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                destination++;
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	    }
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            stack.pop();	
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        }	
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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, source;
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        Scanner scanner = null;
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```
 	try
```
```
        {
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	    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();

```
 
```

            System.out.println("Enter the source for the graph");

            source = scanner.nextInt();

```
 
```

            CheckCycle checkCycle = new CheckCycle();

            checkCycle.dfs(adjacency_matrix, source);

```
 
```

        }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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        scanner.close();	
```
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    }	
```
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}
```

$javac CheckCycle.java
$java CheckCycle
Enter the number of nodes in the graph
5
Enter the adjacency matrix
0 0 0 1 0
1 0 1 0 0
0 0 0 0 0
0 1 0 0 1 
0 0 1 0 0 
Enter the source for the graph
1
The Graph contains a cycle

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