First (unsuccessful) attempt at day 7.1.

2018/internal/tree/tree.go

@@ -0,0 +1,67 @@
+package tree
+
+import (
+	"regexp"
+	"sort"
+)
+
+type Node struct {
+	Name     rune
+	Parents  []*Node
+	Children []*Node
+}
+
+// BuildDependencyTree parses the input and returns the root node.
+func BuildDependencyTree(data []string) *Node {
+	depMap := make(map[rune]*Node)
+	parentRegex := regexp.MustCompile("Step ([A-Z]) must")
+	childRegex := regexp.MustCompile("step ([A-Z]) can begin")
+
+	for _, line := range data {
+		parent := rune(parentRegex.FindSubmatch([]byte(line))[1][0])
+		child := rune(childRegex.FindSubmatch([]byte(line))[1][0])
+
+		// Create the nodes if they don't exist
+		if depMap[parent] == nil {
+			depMap[parent] = &Node{Name: parent}
+		}
+		if depMap[child] == nil {
+			depMap[child] = &Node{Name: child}
+		}
+
+		// Get each node and add the dependency info.
+		pNode := depMap[parent]
+		cNode := depMap[child]
+
+		pNode.Children = append(pNode.Children, cNode)
+		cNode.Parents = append(cNode.Parents, pNode)
+	}
+
+	// sort the children in each node
+	for _, node := range depMap {
+		sortChildren(node)
+	}
+
+	return BuildTreeRoot(depMap)
+}
+
+func sortChildren(node *Node) {
+	children := node.Children
+	sort.Slice(children[:], func(i, j int) bool {
+		return children[i].Name < children[j].Name
+	})
+}
+
+func BuildTreeRoot(depMap map[rune]*Node) *Node {
+	root := &Node{Name: 0}
+
+	for _, node := range depMap {
+		if len(node.Parents) == 0 {
+			root.Children = append(root.Children, node)
+			node.Parents = append(node.Parents, root)
+		}
+	}
+
+	sortChildren(root)
+	return root
+}