transforming nodes

problem.kt

// following data classes are available, feel free to create more if necessary

data class Node(
    val id: String,
    val parentId: String? = null, // nullable string , default null
    val repeat: Int? = null // nullable int , default null
)

data class TargetNode(
    val id: String, // this id's can be generated somehow
    val parentId: String? = null,
    val path: String? = null
)


// main method 1

fun main(args: Array<String>) {
    val nodes = listOf(
        // The list can be in random order
        // for the sake of understanding the problem I left it in order.
        Node("w1"),
        Node("w2", "w1", 2),
        Node("w3", "w1"),
        Node("w4", "w3", 2),
    )
    nodes.forEach {
        println(it)
    }
    transform(nodes).forEach {
        println(it)
    }
}

// output:
Node(id=w1, parentId=null, repeat=null)
Node(id=w2, parentId=w1, repeat=2)
Node(id=w3, parentId=w1, repeat=null)
Node(id=w4, parentId=w3, repeat=2)
TargetNode(id=1, parentId=null, path=null)
--TargetNode(id=2, parentId=1, path=w2+0)
--TargetNode(id=3, parentId=1, path=w2+1)
--TargetNode(id=4, parentId=1, path=null)
----TargetNode(id=5, parentId=4, path=w4+0)
----TargetNode(id=6, parentId=4, path=w4+1)

// different setup of nodes in main method:
fun main(args: Array<String>) {
    val nodes = listOf(
        Node("w1"),
        Node("w2", "w1", 2),
        Node("w3", "w2"), // changed
        Node("w4", "w3", 2),
    )
    nodes.forEach {
        println(it)
    }
    transform(nodes).forEach {
        println(it)
    }
}

// output:
Node(id=w1, parentId=null, repeat=null)
Node(id=w2, parentId=w1, repeat=2)
Node(id=w3, parentId=w2, repeat=null)
Node(id=w4, parentId=w3, repeat=2)
TargetNode(id=1, parentId=null, path=null)
--TargetNode(id=2, parentId=1, path=w2+0)
----TargetNode(id=4, parentId=2, path=w2+0)
------TargetNode(id=6, parentId=4, path=w2+0->w4+0)
------TargetNode(id=7, parentId=4, path=w2+0->w4+1)
--TargetNode(id=3, parentId=1, path=w2+1)
----TargetNode(id=5, parentId=3, path=w2+1)
------TargetNode(id=8, parentId=5, path=w2+1->w4+0)
------TargetNode(id=9, parentId=5, path=w2+1->w4+1)

// Task: write a transform method that's creating the target nodes, so that the output equals the given output
// requirement: 
//   * no recursion, if possible
//   * as less iterations as possible



// Repeated Root Node:

Node(id=w2, parentId=w1, repeat=2)
Node(id=w4, parentId=w3, repeat=2)
Node(id=w1, parentId=null, repeat=3)
Node(id=w3, parentId=w1, repeat=null)

TargetNode(id=1, parentId=null, path=w1+0)
--TargetNode(id=4, parentId=1, path=w1+0->w2+0)
--TargetNode(id=5, parentId=1, path=w1+0->w2+1)
--TargetNode(id=6, parentId=1, path=w1+0)
----TargetNode(id=13, parentId=6, path=w1+0->w4+0)
----TargetNode(id=14, parentId=6, path=w1+0->w4+1)
TargetNode(id=2, parentId=null, path=w1+1)
--TargetNode(id=7, parentId=2, path=w1+1->w2+0)
--TargetNode(id=8, parentId=2, path=w1+1->w2+1)
--TargetNode(id=9, parentId=2, path=w1+1)
----TargetNode(id=15, parentId=9, path=w1+1->w4+0)
----TargetNode(id=16, parentId=9, path=w1+1->w4+1)
TargetNode(id=3, parentId=null, path=w1+2)
--TargetNode(id=10, parentId=3, path=w1+2->w2+0)
--TargetNode(id=11, parentId=3, path=w1+2->w2+1)
--TargetNode(id=12, parentId=3, path=w1+2)
----TargetNode(id=17, parentId=12, path=w1+2->w4+0)
----TargetNode(id=18, parentId=12, path=w1+2->w4+1)