Right view of Binary Tree using Queue

Given a Binary Tree, print Right view of it. Right view of a Binary Tree is set of nodes visible when tree is visited from Right side. 

Examples:

Input : 
              10
            /     \
          2         3
        /   \    /    \
       7     8  12     15
                      /
                    14
Output : 10 3 15 14
The output nodes are the rightmost
nodes of their respective levels.

We have already discussed recursive solution for right view. In this post, level order traversal based solution is discussed. 
If we observe carefully, we will see that our main task is to print the right most node of every level. So, we will do a level order traversal on the tree and print the rightmost node at every level.

Below is the implementation of above approach: 

C++

// C++ program to print right view of
// Binary Tree

#include<bits/stdc++.h>
using namespace std;

// A Binary Tree Node
struct Node
{
    int data;
    struct Node *left, *right;
};

// Utility function to create a new tree node
Node* newNode(int data)
{
    Node *temp = new Node;
    temp->data = data;
    temp->left = temp->right = NULL;
    return temp;
}

// function to print right view of
// binary tree
void printRightView(Node* root)
{
    if (!root)
        return;

    queue<Node*> q;
    q.push(root);

    while (!q.empty())
    {
        // number of nodes at current level
        int n = q.size();

        // Traverse all nodes of current level
        for(int i = 1; i <= n; i++)
        {
            Node* temp = q.front();
            q.pop();

            // Print the right most element
            // at the level
            if (i == n)
                cout<<temp->data<<" ";

            // Add left node to queue
            if (temp->left != NULL)
                q.push(temp->left);

            // Add right node to queue
            if (temp->right != NULL)
                q.push(temp->right);
        }
    }
}

// Driver program to test above functions
int main()
{
    // Let's construct the tree as
    // shown in example

    Node* root = newNode(10);
    root->left = newNode(2);
    root->right = newNode(3);
    root->left->left = newNode(7);
    root->left->right = newNode(8);
    root->right->right = newNode(15);
    root->right->left = newNode(12);
    root->right->right->left = newNode(14);

    printRightView(root);
}

Java

// Java program to print right view of Binary
// Tree
import java.util.*;

public class PrintRightView
{
    // Binary tree node
    private static class Node
    {
        int data;
        Node left, right;

        public Node(int data) {
            this.data = data;
            this.left = null;
            this.right = null;
        }
    }

    // function to print right view of binary tree
    private static void printRightView(Node root)
    {
        if (root == null)
            return;

        Queue<Node> queue = new LinkedList<>();
        queue.add(root);

        while (!queue.isEmpty())
        {
            // number of nodes at current level
            int n = queue.size();

            // Traverse all nodes of current level
            for (int i = 1; i <= n; i++) {
                Node temp = queue.poll();

                // Print the right most element at
                // the level
                if (i == n)
                    System.out.print(temp.data + " ");

                // Add left node to queue
                if (temp.left != null)
                    queue.add(temp.left);

                // Add right node to queue
                if (temp.right != null)
                    queue.add(temp.right);
            }
        }
    }

    // Driver code
    public static void main(String[] args)
    {
        // construct binary tree as shown in
        // above diagram
        Node root = new Node(10);
        root.left = new Node(2);
        root.right = new Node(3);
        root.left.left = new Node(7);
        root.left.right = new Node(8);
        root.right.right = new Node(15);
        root.right.left = new Node(12);
        root.right.right.left = new Node(14);

        printRightView(root);
    }
}

Python3

# Python3 program to print right view of
# Binary Tree

# Binary Tree Node
""" utility that allocates a newNode
with the given key """
class newNode:

    # Construct to create a newNode
    def __init__(self, key):
        self.data = key
        self.left = None
        self.right = None
        self.hd = 0

# function to print right view of
# binary tree
def printRightView(root):

    if (not root):
        return

    q = []
    q.append(root)

    while (len(q)):

        # number of nodes at current level
        n = len(q)

        # Traverse all nodes of current level
        for i in range(1, n + 1):
            temp = q[0]
            q.pop(0)

            # Print the right most element
            # at the level
            if (i == n) :
                print(temp.data, end = " " )

            # Add left node to queue
            if (temp.left != None) :
                q.append(temp.left)

            # Add right node to queue
            if (temp.right != None) :
                q.append(temp.right)

# Driver Code
if __name__ == '__main__':

    root = newNode(10)
    root.left = newNode(2)
    root.right = newNode(3)
    root.left.left = newNode(7)
    root.left.right = newNode(8)
    root.right.right = newNode(15)
    root.right.left = newNode(12)
    root.right.right.left = newNode(14)
    printRightView(root)

# This code is contributed by
# Shubham Singh(SHUBHAMSINGH10)

C#

// C# program to print right view
// of Binary Tree
using System;
using System.Collections.Generic;

public class PrintRightView
{
    // Binary tree node
    private class Node
    {
        public int data;
        public Node left, right;

        public Node(int data)
        {
            this.data = data;
            this.left = null;
            this.right = null;
        }
    }

    // function to print right view of binary tree
    private static void printRightView(Node root)
    {
        if (root == null)
            return;

        Queue<Node> queue = new Queue<Node>();
        queue.Enqueue(root);

        while (queue.Count != 0)
        {
            // number of nodes at current level
            int n = queue.Count;

            // Traverse all nodes of current level
            for (int i = 1; i <= n; i++)
            {
                Node temp = queue.Dequeue();

                // Print the right most element at
                // the level
                if (i == n)
                    Console.Write(temp.data + " ");

                // Add left node to queue
                if (temp.left != null)
                    queue.Enqueue(temp.left);

                // Add right node to queue
                if (temp.right != null)
                    queue.Enqueue(temp.right);
            }
        }
    }

    // Driver code
    public static void Main(String[] args)
    {
        // construct binary tree as shown in
        // above diagram
        Node root = new Node(10);
        root.left = new Node(2);
        root.right = new Node(3);
        root.left.left = new Node(7);
        root.left.right = new Node(8);
        root.right.right = new Node(15);
        root.right.left = new Node(12);
        root.right.right.left = new Node(14);
        printRightView(root);
    }
}

// This code is contributed 29AjayKumar

Javascript

<script>

// JavaScript program to print right view
// of Binary Tree
// Binary tree node
class Node
{
    constructor(data)
    {
        this.data = data;
        this.left = null;
        this.right = null;
    }
}

// function to print right view of binary tree
function printRightView(root)
{
    if (root == null)
        return;

    var queue = [];
    queue.push(root);

    while (queue.length != 0)
    {
        // number of nodes at current level
        var n = queue.length;

        // Traverse all nodes of current level
        for (var i = 1; i <= n; i++)
        {
            var temp = queue.shift();

            // Print the right most element at
            // the level
            if (i == n)
                document.write(temp.data + " ");

            // Add left node to queue
            if (temp.left != null)
                queue.push(temp.left);

            // Add right node to queue
            if (temp.right != null)
                queue.push(temp.right);
        }
    }
}
// Driver code
// construct binary tree as shown in
// above diagram
var root = new Node(10);
root.left = new Node(2);
root.right = new Node(3);
root.left.left = new Node(7);
root.left.right = new Node(8);
root.right.right = new Node(15);
root.right.left = new Node(12);
root.right.right.left = new Node(14);
printRightView(root);

</script>

Output

10 3 15 14 

Time Complexity: O( n ), where n is the number of nodes in the binary tree. 
Auxiliary Space: O( n ) for Queue Data Structure