Thread: Breadth first Search:

I have done this before in C++ but now I want to do it in Java. I am not sure how to iterate through a ArrayList, I have look several places because lets be honest the first stop is normally google. I tried the examples but with no luck. I was hoping to find a fixed work like

 
for(auto it= foo.begin(); it!= foo.end(); foo++)
{
        *it //do something.
}

Here is the program:

 
package org.search.BFS;
 
import java.util.Queue;
 
 
public class BFS extends Graph
{
	private Queue<Integer> q;
 
 
	BFS(int s)
	{
		//mark all the vertices as not visited
		boolean[] visited = new boolean[V];
 
		for(int i=0; i <V; i++)
		{
			visited[i]=false;
		}
 
		//mark the current node as visited and enqueue it
		visited[s]=true;
		q.add(s);
 
 
 
		while(!q.isEmpty())
		{
			//Dequeue a vertex from queue and print it
			 s=q.poll();// gets front of queue
			 System.out.println(s);
			 q.remove();//popping front off queue
 
                  //************************************************
			 //I want to iterate doing something like
                        for(auto = adj[s].begin(); i != adj[s].end(); ++i)         
                //*************************************************
		}
 
	}
 
 
}

package org.search.BFS;
 
import java.util.ArrayList;
 
public class Graph 
{
	protected int V;
	ArrayList<Integer>[] adj; //array containing adjacency lists
 
	Graph()
	{
 
	}
 
	Graph(int V) //constructor
	{
		this.V = V;
		adj = new ArrayList[V];
	}
 
	void addEdge(int v, int w)
	{
		adj[v].add(w);
	}
 
}

Also the below is giving me a Type safety: The expression of type ArrayList[] needs unchecked conversation to conform to ArrayList<Integer>[]

adj = new ArrayList[V];

What does this mean?

This is how you construct an ArrayList in java:

List<Integer> myIntList = new ArrayList<>();

you can not use brackets "[]" on anything but primitive arrays.

If you want to iterate a list there are 2 possibilities, iterate with an index variable:

for (int id = 0; id < myIntList.size(); id++) {
     Integer element = myIntList.get(id);
}

or a for-each loop over the elements:

for (Integer element : myIntList) {...}

Or, you can learn about the Java Collections Framework and the Iterator options it provides.

Thank you...