BFS Algorithm Implementation in Kotlin

BFS.kt

object BFS {
    @JvmStatic
    fun main(args: Array<String>) {
        val station1 = Node("Westminster", null, null)
        val station2 = Node("Waterloo", station1, null)
        val station3 = Node("Trafalgar Square", station1, station2)
        val station4 = Node("Canary Wharf", station2, station3)
        val station5 = Node("London Bridge", station4, station3)
        val station6 = Node("Tottenham Court Road", station5, station4)
        val bfs = BreadthFirstSearch(station6, station3)
        print("Path Found:: ${bfs.compute()}")
    }
}

/**
 * Class that represent a node by following a UID, firstChild and secondChild.
 * Provide public API to get child as a list [getChildren].
 */
class Node(val id: String, private val firstChild: Node? = null, private val secondChild: Node? = null) {
    fun getChildren(): MutableList<Node> {
        val list = mutableListOf<Node>()
        firstChild?.let { list.add(it) }
        secondChild?.let { list.add(it) }
        return list
    }
}

/**
 * Class that represent the Breadth First Algorithm.
 *
 * @param startNode [Node] from where the search will start.
 * @param goalNode [Node] to be found.
 */
class BreadthFirstSearch(private val startNode: Node, private val goalNode: Node) {
    fun compute(): Boolean {
        // Check if the start and goal is the same or not.
        if (startNode.id == goalNode.id) {
            return true
        }
        // Create a new Queue and ArrayList to hold traversed and visited nodes.
        val queue: Queue<Node> = LinkedList()
        val explored: ArrayList<Node> = arrayListOf()

        // Add start node as the entry point and mark as visited.
        queue.add(startNode)
        explored.add(startNode)

        // Start finding the goal node from the Queue.
        while (!queue.isEmpty()) {
            // First current node remove from the Queue.
            val current = queue.remove()
            // Check if matches or not.
            if (current.id == goalNode.id) {
                return true
            } else {
                // Check if it has child nodes or not.
                // If it has, start the searching process again.
                if (current.getChildren().isEmpty()) {
                    return false
                } else {
                    queue.addAll(current.getChildren())
                }
            }
            explored.add(current)
        }
        return false
    }
}