Right view of binary tree

Problem: Right view of a binary tree is set of nodes visible when tree is visited from right side. Write a program to print the right view of a binary tree.

Example:

Input: root = [1,2,3,null,5,null,4]
Output: [1,3,4]

Input: root = [1,null,3]
Output: [1,3]

Input: root = []
Output: []

Approach: Do level order traversal and print the last node in every level.


Implementation in C#:

    public IList<int> RightSideView(TreeNode root)

    {

        List<int> result = new List<int>();

        if (root == null)

        {

            return result;

        }

        Queue<TreeNode> queue = new Queue<TreeNode>();

        queue.Enqueue(root);

        while (queue.Count != 0)

        {

            int size = queue.Count;

            TreeNode rightNode = null;

            for (int i = 0; i < size; ++i)

            {

                rightNode = queue.Dequeue();

                if (rightNode.left != null)

                {

                    queue.Enqueue(rightNode.left);

                }

                if (rightNode.right != null)

                {

                    queue.Enqueue(rightNode.right);

                }

            }

            result.Add(rightNode.val);

        }

        return result;

    }        

Complexity: O(n)