First (unsuccessful) attempt at day 7.1.

2018/internal/tree/findorder.go

@@ -0,0 +1,51 @@
+package tree
+
+import "fmt" // debug
+
+// FindOrder determines the correct order according to these rules:
+// 1. A node cannot come before all of its parents have been included.
+// 2. At any given time, the lowest-lettered step must be executed.
+func FindOrder(root *Node) []*Node {
+	seen := make(map[rune]bool)
+	return findOrderR(root, seen)
+}
+
+func findOrderR(node *Node, seen map[rune]bool) []*Node {
+	order := []*Node{}
+
+	// debug
+	fmt.Printf("In node: %c | Children: ", node.Name)
+	for _, child := range node.Children {
+		fmt.Printf("%c ", child.Name)
+	}
+	fmt.Printf("| Parents: ")
+	for _, parent := range node.Parents {
+		fmt.Printf("%c ", parent.Name)
+	}
+	fmt.Println()
+	// end debug
+
+	// add the node, but only if all its parents have been seen
+	if len(node.Parents) == 0 {
+		seen[node.Name] = true
+	} else {
+		for _, parent := range node.Parents {
+			if _, ok := seen[parent.Name]; !ok {
+				return order
+			}
+		}
+
+		if _, ok := seen[node.Name]; !ok {
+			order = append(order, node)
+			fmt.Printf("Added node: %c\n", node.Name)
+			seen[node.Name] = true
+		}
+	}
+
+	// recurse
+	for _, child := range node.Children {
+		order = append(order, findOrderR(child, seen)...)
+	}
+
+	return order
+}