Given a list of tickets, find itinerary in order using the given list.

SortFlight.java

// A Java program to print topological sorting of a DAG
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
		// vertex
		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(5);
		// Chennai - 0
		// Goa - 1
		// Delhi - 2
		// Bombay - 3
		// Bangalore - 4
		g.addEdge(0, 4);
		g.addEdge(1, 0);
		g.addEdge(2, 1);
		g.addEdge(3, 2);
		
		System.out.println("Following is a Topological " +
						"sort of the given graph");
		g.topologicalSort();
	}
}