Binary Tree - BFS [199. Binary Tree Right Side View]

    fun rightSideView(root: TreeNode?): List<Int> {
        // Create a list to store the rightmost values
        val rightmostValues = mutableListOf<Int>()

        // Check if the root is null, if so, return the empty list
        if (root == null) return rightmostValues

        // Create a queue to perform BFS
        val queue: Queue<TreeNode> = LinkedList()
        queue.offer(root)

        // Perform BFS
        while (queue.isNotEmpty()) {
            // Get the number of nodes at the current level
            val levelSize = queue.size

            // Variable to store the rightmost node at the current level
            var rightmostNode: TreeNode? = null

            // Process all nodes at the current level
            repeat(levelSize) {
                // Get the node from the front of the queue
                val node = queue.poll()

                // Update the rightmost node
                rightmostNode = node

                // Add the left and right child nodes to the queue if they exist
                node.left?.let { queue.offer(it) }
                node.right?.let { queue.offer(it) }
            }

            // Add the value of the rightmost node to the list
            rightmostNode?.let { rightmostValues.add(it.`val`) }
        }

        // Return the list of rightmost values
        return rightmostValues
    }