Add WIP LeafCounter which calculates the height of each node without recursion

Currently is very slow though due to dealing with a lot of height 1 nodes. Maybe the default should be 1 and we should track completed nodes instead?

Author: MaartenS11

src/main/kotlin/be/ugent/topl/mio/ui/LeafCounter.kt

@@ -0,0 +1,39 @@
+package be.ugent.topl.mio.ui
+
+import be.ugent.topl.mio.debugger.MultiverseGraph
+import be.ugent.topl.mio.debugger.MultiverseNode
+
+class LeafCounter(private val graph: MultiverseGraph) {
+    private val cachedHeights = mutableMapOf<MultiverseNode, Int>()
+
+    // TODO: Maybe it only needs to update changed nodes.
+    fun calculateLeafCounts() {
+        println("Calculating leaf counts")
+        val time = System.currentTimeMillis()
+        cachedHeights.clear()
+        val stack = mutableListOf(graph.rootNode)
+        while (stack.isNotEmpty()) {
+            val currentNode = stack.last()
+            if (currentNode.children.isEmpty()) {
+                cachedHeights[currentNode] = 1
+            }
+            // We already calculated the height of our children -> calculate our height!
+            else if (cachedHeights.contains(currentNode.children.first())) {
+                var heightSum = 0
+                for (child in currentNode.children) {
+                    heightSum += cachedHeights[child]!!
+                }
+                cachedHeights[currentNode] = heightSum
+            }
+            if (cachedHeights.containsKey(currentNode)) {
+                stack.removeLast()
+            }
+            stack.addAll(currentNode.children)
+        }
+        println("Finished calculating leaf counts ${System.currentTimeMillis() - time} ms elapsed")
+    }
+
+    fun getLeafCount(node: MultiverseNode): Int {
+        return cachedHeights[node]!!
+    }
+}