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Topological Sort in Java #254

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83 changes: 83 additions & 0 deletions Sorts/TopologicalSort.java
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import java.io.*;
import java.util.*;

// This class represents a directed graph using adjacency
// list representation
class Graph
{
private int V; // No. of vertices
private LinkedList<Integer> adj[]; // Adjacency List

//Constructor
Graph(int v)
{
V = v;
adj = new LinkedList[v];
for (int i=0; i<v; ++i)
adj[i] = new LinkedList();
}

// Function to add an edge into the graph
void addEdge(int v,int w) { adj[v].add(w); }

// A recursive function used by topologicalSort
void topologicalSortUtil(int v, boolean visited[],
Stack stack)
{
// Mark the current node as visited.
visited[v] = true;
Integer i;

// Recur for all the vertices adjacent to this
Iterator<Integer> it = adj[v].iterator();
while (it.hasNext())
{
i = it.next();
if (!visited[i])
topologicalSortUtil(i, visited, stack);
}

// Push current vertex to stack which stores result
stack.push(new Integer(v));
}

// The function to do Topological Sort. It uses
// recursive topologicalSortUtil()
void topologicalSort()
{
Stack stack = new Stack();

// Mark all the vertices as not visited
boolean visited[] = new boolean[V];
for (int i = 0; i < V; i++)
visited[i] = false;

// Call the recursive helper function to store
// Topological Sort starting from all vertices
// one by one
for (int i = 0; i < V; i++)
if (visited[i] == false)
topologicalSortUtil(i, visited, stack);

// Print contents of stack
while (stack.empty()==false)
System.out.print(stack.pop() + " ");
}

// Driver method
public static void main(String args[])
{
// Create a graph given in the above diagram
Graph g = new Graph(6);
g.addEdge(5, 2);
g.addEdge(5, 0);
g.addEdge(4, 0);
g.addEdge(4, 1);
g.addEdge(2, 3);
g.addEdge(3, 1);

System.out.println("Following is a Topological " +
"sort of the given graph");
g.topologicalSort();
}
}