Add BottomView.java

Program to print bottom view of a binary tree.

Author: rajniarora26

BottomView.java

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+// Java Program to print Bottom View of Binary Tree
+import java.util.*;
+import java.util.Map.Entry;
+
+// Tree node class
+class Node
+{
+	int data; //data of the node
+	int hd; //horizontal distance of the node
+	Node left, right; //left and right references
+
+	// Constructor of tree node
+	public Node(int key)
+	{
+		data = key;
+		hd = Integer.MAX_VALUE;
+		left = right = null;
+	}
+}
+
+//Tree class
+class Tree
+{
+	Node root; //root node of tree
+
+	// Default constructor
+	public Tree() {}
+
+	// Parameterized tree constructor
+	public Tree(Node node)
+	{
+		root = node;
+	}
+
+	// Method that prints the bottom view.
+	public void bottomView()
+	{
+		if (root == null)
+			return;
+
+		// Initialize a variable 'hd' with 0 for the root element.
+		int hd = 0;
+
+		// TreeMap which stores key value pair sorted on key value
+		Map<Integer, Integer> map = new TreeMap<>();
+
+		// Queue to store tree nodes in level order traversal
+		Queue<Node> queue = new LinkedList<Node>();
+
+		// Assign initialized horizontal distance value to root
+		// node and add it to the queue.
+		root.hd = hd;
+		queue.add(root);
+
+		// Loop until the queue is empty (standard level order loop)
+		while (!queue.isEmpty())
+		{
+			Node temp = queue.remove();
+
+			// Extract the horizontal distance value from the
+			// dequeued tree node.
+			hd = temp.hd;
+
+			// Put the dequeued tree node to TreeMap having key
+			// as horizontal distance. Every time we find a node
+			// having same horizontal distance we need to replace
+			// the data in the map.
+			map.put(hd, temp.data);
+
+			// If the dequeued node has a left child add it to the
+			// queue with a horizontal distance hd-1.
+			if (temp.left != null)
+			{
+				temp.left.hd = hd-1;
+				queue.add(temp.left);
+			}
+			// If the dequeued node has a right child add it to the
+			// queue with a horizontal distance hd+1.
+			if (temp.right != null)
+			{
+				temp.right.hd = hd+1;
+				queue.add(temp.right);
+			}
+		}
+
+		// Extract the entries of map into a set to traverse
+		// an iterator over that.
+		Set<Entry<Integer, Integer>> set = map.entrySet();
+
+		// Make an iterator
+		Iterator<Entry<Integer, Integer>> iterator = set.iterator();
+
+		// Traverse the map elements using the iterator.
+		while (iterator.hasNext())
+		{
+			Map.Entry<Integer, Integer> me = iterator.next();
+			System.out.print(me.getValue()+" ");
+		}
+	}
+}
+
+// Main driver class
+public class BottomView
+{
+	public static void main(String[] args)
+	{
+		Node root = new Node(20);
+		root.left = new Node(8);
+		root.right = new Node(22);
+		root.left.left = new Node(5);
+		root.left.right = new Node(3);
+		root.right.left = new Node(4);
+		root.right.right = new Node(25);
+		root.left.right.left = new Node(10);
+		root.left.right.right = new Node(14);
+		Tree tree = new Tree(root);
+		System.out.println("Bottom view of the given binary tree:");
+		tree.bottomView();
+	}
+}