add factory method newAntiNodeCache()

day-08/internal/one/graph.go

@@ -12,6 +12,10 @@ type graph struct {
 	antinodes map[coords]struct{}
 }
 
+func newGraph() *graph {
+	return &graph{antinodes: make(map[coords]struct{})}
+}
+
 func (g *graph) String() string {
 	return strings.Join(g.data, "\n")
 }

day-08/internal/one/solve.go

@@ -14,8 +14,6 @@ func Solve(buf []byte) (int, error) {
 		return 0, err
 	}
 
-	graph.antinodes = make(map[coords]struct{})
-
 	for i, a := range graph.antennae {
 		for j, b := range graph.antennae {
 			if i == j || a.identifier != b.identifier {

day-08/internal/one/util.go

@@ -9,7 +9,7 @@ import (
 var reMatchAntennae = regexp.MustCompile(`[a-zA-Z0-9]`)
 
 func parseLines(r io.Reader) (*graph, error) {
-	var graph graph
+	graph := newGraph()
 
 	var linecount int
 	scanner := bufio.NewScanner(r)
@@ -30,5 +30,5 @@ func parseLines(r io.Reader) (*graph, error) {
 		return nil, err
 	}
 
-	return &graph, nil
+	return graph, nil
 }

day-08/internal/two/graph.go

@@ -13,7 +13,7 @@ type graph struct {
 }
 
 func newGraph() *graph {
-	return &graph{[]string{}, []antenna{}, newAntiNodeCache()}
+	return &graph{antinodes: newAntiNodeCache()}
 }
 
 func (g *graph) String() string {