Day 7.2 solution.

2018/internal/tree/tree.go

@@ -9,6 +9,7 @@ type Node struct {
 	Name     rune
 	Parents  []*Node
 	Children []*Node
+	Worked   int // the amount of time spent working on this node.
 }
 
 // BuildDependencyTree parses the input and returns the root node.