Add day 6 part 1 in Kotlin

2019/06/day06.kt

@@ -0,0 +1,13 @@
+fun main() {
+    val input = generateSequence(::readLine)
+        .map { it.split(")") }
+        .groupBy { it[0] }
+        .mapValues{ it.value.map { it[1] } }
+    val rootNode = input.keys - input.values.flatten().toSet()
+    
+    println("Part 1: ${countOrbiters(input, rootNode.first(), 0)}")
+}
+
+fun <T>countOrbiters(graph: Map<T, List<T>>, key: T, acc: Int): Int {
+    return acc + (graph[key]?.map { countOrbiters(graph, it, acc+1) }?.sum() ?: 0)
+}