CC-2 : Implement Breadth First traversal of Binary Tree.

Description:

Implement and test a Breadth First Traversal of Binary Tree (using iterative method).

Test cases and expected outputs:

Input Parameters	Expected outputs
	Bfs traversal : 4, 5 ,7, 6, 78, 14, 33, 8, 16, 18, 9

Pseudocode:

Define an ArrayList to hold the nodes traversed while doing Breadth First traversal.

Define a Queue to temporarily hold Tree nodes as we do Breadth First traversal.

Add the root node of the Tree to the Queue.

While Queue size is not zero:

Extract a Tree node from the Queue.

Add the data of the current Tree node to the ArrayList.

If left child node of current Tree node is not null, add it to the Queue.

If right child node of current Tree node is not null, add it to the Queue.

Return the Array list as it contains the data of the nodes of the Tree in Breadth First order.

Code:

public ArrayList<Integer> bfsTraversal(BinTreeNode root) throws Exception{
	if (root==null) {return null;}
	ArrayList<Integer> bfs=new ArrayList<Integer>();
	Queue<BinTreeNode> queue=new LinkedList<BinTreeNode>();
	queue.offer(root);
	BinTreeNode node=null;
	while (queue.size()!=0) {
		node=queue.poll();
		bfs.add(node.getNodeData());
		if (node.getLeftChild()!=null) {
			queue.offer(node.getLeftChild());
		}	
		if (node.getRightChild()!=null) {
			queue.offer(node.getRightChild());
		}
			
	}
	return bfs;
}

Click here to download and run code and test cases !

Below fully running code can be copied and run on Eclipse or other Java IDEs. Refer the classname in code below. If the class name below is "A", save the code below to a file named A.java before running it. Be sure to try your own test cases to enhance your understanding ! You can also tweak the code to optimize or add enhancements and custom features.

Note: for easy reference BinTreeNode is included as internal class in program below. Ideally it should be in a separate file.

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.Queue;


public class BinTreeBFSTraversal {	

public ArrayList<Integer> bfsTraversal(BinTreeNode root) throws Exception{
	if (root==null) {return null;}
	ArrayList<Integer> bfs=new ArrayList<Integer>();
	Queue<BinTreeNode> queue=new LinkedList<BinTreeNode>();
	queue.offer(root);
	BinTreeNode node=null;
	while (queue.size()!=0) {
		node=queue.poll();
		bfs.add(node.getNodeData());
		if (node.getLeftChild()!=null) {
			queue.offer(node.getLeftChild());
		}	
		if (node.getRightChild()!=null) {
			queue.offer(node.getRightChild());
		}
			
	}
	return bfs;
}

public static void printArrayListSummary(ArrayList al, String label) throws Exception {
	if (al == null) { System.out.println("\n\n Input ArrayList was null !! \n"); return; }
	System.out.println();
	System.out.println("***********************************************************************");
	System.out.print(label+" : ");
	int arrayIndex=0;
	for (arrayIndex=0; arrayIndex < al.size(); arrayIndex++) {
			System.out.print(al.get(arrayIndex));
			if (arrayIndex < al.size()-1) {System.out.print(",");}
	} 
	System.out.println();
	System.out.println("************************************************************************");
		System.out.println();
		Thread.sleep(2000);
		return;
}
 	
public static void main(String[] args) {
	/***********************
	 Test cases given below:
	 **********************/
	ArrayList<Integer> retVal=null;
	try {
	BinTreeBFSTraversal bfs=new BinTreeBFSTraversal();	
	BinTreeNode root=bfs.new BinTreeNode(4);
	//Left L1 Children
	root.setLeftChild(bfs.new BinTreeNode(5));
	root.setRightChild(bfs.new BinTreeNode(7));
	
	//Left L2 Children
	root.getLeftChild().setLeftChild(bfs.new BinTreeNode(6));
	root.getLeftChild().setRightChild(bfs.new BinTreeNode(78));
	
	//Left L3 Children
	root.getLeftChild().getLeftChild().setLeftChild(bfs.new BinTreeNode(33));
	
	//Right L2 Children
	root.getRightChild().setLeftChild(bfs.new BinTreeNode(14));	
	
	//Right L3 Children
	root.getRightChild().getLeftChild().setLeftChild(bfs.new BinTreeNode(8));
	root.getRightChild().getLeftChild().setRightChild(bfs.new BinTreeNode(16));
	
	//Right L3 Children
	root.getRightChild().getLeftChild().getRightChild().setLeftChild(bfs.new BinTreeNode(18));
	
	//Right L4 Children
	root.getRightChild().getLeftChild().getRightChild().getLeftChild().setLeftChild(bfs.new BinTreeNode(9));
	
	retVal=bfs.bfsTraversal(root);
	printArrayListSummary(retVal, "Bfs traversal");	
	
	}catch (Exception exception) {
	System.out.print("Exception: "+ exception);
	exception.printStackTrace();
	}
		
	}

class BinTreeNode {
	private BinTreeNode leftNode=null;
	private BinTreeNode rightNode=null;
	private int nodeData=0;
	
	public BinTreeNode(int data) {
		nodeData=data;
	}	
	public BinTreeNode getLeftChild() {
		return leftNode;
	}
	public void setLeftChild(BinTreeNode leftNode) {
		this.leftNode = leftNode;
	}
	public BinTreeNode getRightChild() {
		return rightNode;
	}
	public void setRightChild(BinTreeNode rightNode) {
		this.rightNode = rightNode;
	}
	public int getNodeData() {
		return nodeData;
	}
	public void setNodeData(int nodeData) {
		this.nodeData = nodeData;
	}

}
	
}