Right view of Binary Tree using Queue

Last Updated : 26 Sep, 2024

Given a Binary Tree, the task is to print the Right view of it. The right view of a Binary Tree is a set of rightmost nodes for every level.

Examples:

Example 1: The Green colored nodes (1, 3, 5) represents the Right view in the below Binary tree.

Example 2: The Green colored nodes (1, 3, 4, 5) represents the Right view in the below Binary tree.

Approach:

The idea is to traverse the tree level by level and print the last node at each level (the rightmost node). A simple solution is to do level order traversal and print the last node in every level.

Follow the steps below to implement the idea:

Perform a level order traversal of the binary tree.
For each level, print the last node in it's level order traversal.
Move to the next level and repeat until all levels are processed.

Below is the implementation of above approach:

C++

// C++ program to print right view of Binary
// tree using Level order Traversal
#include <bits/stdc++.h>
using namespace std;

class Node {
public:
    int data;
    Node* left;
    Node* right;

    Node(int x) {
        data = x;
        left = right = nullptr;
    }
};

// Function to return the right view of the binary tree
vector<int> rightView(Node* root) {
    vector<int> result;

    if (root == nullptr) return result;

    // Queue for level order traversal
    queue<Node*> q;
    q.push(root);

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

        for (int i = 0; i < levelSize; i++) {
            Node* curr = q.front();
            q.pop();

            // If it's the last node of the current level
            if (i == levelSize - 1) {
                result.push_back(curr->data);
            }

            // Enqueue left child
            if (curr->left != nullptr) {
                q.push(curr->left);
            }

            // Enqueue right child
            if (curr->right != nullptr) {
                q.push(curr->right);
            }
        }
    }

    return result;
}

void printArray(vector<int>& arr) {
    for (int val : arr) {
        cout << val << " ";
    }
    cout << endl;
}

int main() {
  
    // Representation of the input tree:
    //         1
    //        / \
    //       2   3
    //          / \   
    //         4   5 
    Node* root = new Node(1);
    root->left = new Node(2);
    root->right = new Node(3);
    root->right->left = new Node(4);
    root->right->right = new Node(5);

    vector<int> result = rightView(root);
    
    printArray(result);
    
    return 0;
}

Java

// Java program to print right view of Binary
// tree using Level order Traversal
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.Queue;

class Node {
    int data;
    Node left, right;

    Node(int x) {
        data = x;
        left = right = null;
    }
}

class GfG {

    // Function to return the right view of the binary tree
    static ArrayList<Integer> rightView(Node root) {
        ArrayList<Integer> result = new ArrayList<>();
        
        if (root == null) {
            return result;
        }

        // Queue for level order traversal
        Queue<Node> q = new LinkedList<>();
        q.add(root);

        while (!q.isEmpty()) {
          
            // Number of nodes at the current level
            int levelSize = q.size();

            for (int i = 0; i < levelSize; i++) {
                Node curr = q.poll();

                // If it's the last node of the current level
                if (i == levelSize - 1) {
                    result.add(curr.data);
                }

                // Enqueue left child
                if (curr.left != null) {
                    q.add(curr.left);
                }

                // Enqueue right child
                if (curr.right != null) {
                    q.add(curr.right);
                }
            }
        }

        return result;
    }

    static void printArray(ArrayList<Integer> arr) {
        for (int val : arr) {
            System.out.print(val + " ");
        }
        System.out.println();
    }

    public static void main(String[] args) {

        // Representation of the input tree:
        //         1
        //        / \
        //       2   3
        //          / \   
        //         4   5 
        Node root = new Node(1);
        root.left = new Node(2);
        root.right = new Node(3);
        root.right.left = new Node(4);
        root.right.right = new Node(5);

        ArrayList<Integer> result = rightView(root);

        printArray(result);
    }
}

Python

# Python program to print right view of Binary Tree
# using Level Order Traversal
from collections import deque

class Node:
    def __init__(self, data):
        self.data = data
        self.left = None
        self.right = None

# Function to return the right view of the binary tree
def rightView(root):
    result = []
    
    if root is None:
        return result

    # Queue for level order traversal
    q = deque([root])

    while q:
      
        # Number of nodes at the current level
        level_size = len(q)

        for i in range(level_size):
            curr = q.popleft()

            # If it's the last node of the 
            # current level
            if i == level_size - 1:
                result.append(curr.data)

            # Enqueue left child
            if curr.left is not None:
                q.append(curr.left)

            # Enqueue right child
            if curr.right is not None:
                q.append(curr.right)

    return result

def printArray(arr):
    for val in arr:
        print(val, end=" ")
    print()

if __name__ == "__main__":
    
    # Representation of the input tree:
    #         1
    #        / \
    #       2   3
    #          / \   
    #         4   5 
    root = Node(1)
    root.left = Node(2)
    root.right = Node(3)
    root.right.left = Node(4)
    root.right.right = Node(5)

    result = rightView(root)
    
    printArray(result)

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

class Node {
    public int data;
    public Node left, right;

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

class GfG {
  
    // Function to return the right view of 
    // the binary tree
    static List<int> rightView(Node root) {
        List<int> result = new List<int>();

        if (root == null) {
            return result;
        }

        // Queue for level order traversal
        Queue<Node> queue = new Queue<Node>();
        queue.Enqueue(root);

        while (queue.Count > 0) {
          
            // Number of nodes at the current level
            int levelSize = queue.Count;

            for (int i = 0; i < levelSize; i++) {
                Node curr = queue.Dequeue();

                // If it's the last node of 
                // the current level
                if (i == levelSize - 1) {
                    result.Add(curr.data);
                }

                // Enqueue left child
                if (curr.left != null) {
                    queue.Enqueue(curr.left);
                }

                // Enqueue right child
                if (curr.right != null) {
                    queue.Enqueue(curr.right);
                }
            }
        }

        return result;
    }

    static void PrintList(List<int> arr) {
        foreach (int val in arr) {
            Console.Write(val + " ");
        }
        Console.WriteLine();
    }

    static void Main(string[] args) {
      
        // Representation of the input tree:
        //         1
        //        / \
        //       2   3
        //           / \   
        //          4   5 
        Node root = new Node(1);
        root.left = new Node(2);
        root.right = new Node(3);
        root.right.left = new Node(4);
        root.right.right = new Node(5);

        List<int> result = rightView(root);
        
        PrintList(result);
    }
}

JavaScript

// JavaScript program to print right view of Binary
// tree using Level order Traversal

class Node {
    constructor(data) {
        this.data = data;
        this.left = null;
        this.right = null;
    }
}

// Function to return the right view of the binary tree
function rightView(root) {
    let result = [];

    if (root === null) {
        return result;
    }

    // Queue for level order traversal
    let queue = [root];

    while (queue.length > 0) {
    
        // Number of nodes at the current level
        let levelSize = queue.length;

        for (let i = 0; i < levelSize; i++) {
            let curr = queue.shift();

            // If it's the last node of the 
            // current level
            if (i === levelSize - 1) {
                result.push(curr.data);
            }

            // Enqueue left child
            if (curr.left !== null) {
                queue.push(curr.left);
            }

            // Enqueue right child
            if (curr.right !== null) {
                queue.push(curr.right);
            }
        }
    }

    return result;
}

function printArray(arr) {
    console.log(arr.join(' '));
}

// Representation of the input tree:
//         1
//        / \
//       2   3
//           / \   
//          4   5 
let root = new Node(1);
root.left = new Node(2);
root.right = new Node(3);
root.right.left = new Node(4);
root.right.right = new Node(5);

let result = rightView(root);

printArray(result);

Output

1 3 5

Time Complexity: O(n), We traverse all nodes of the binary tree exactly once, where n is the number of nodes.
Auxiliary Space: O(n) since using auxiliary space for queue.

Related articles:

Print Right View of a Binary Tree

Right view of Binary Tree using Queue

Analysis of Algorithms

Bibhas Abhishek

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