adjust puzzle runner

main.go

@@ -8,7 +8,6 @@ import (
 	"io"
 	"log"
 	"os"
-	"strconv"
 )
 
 type puzzle interface {
@@ -16,32 +15,22 @@ type puzzle interface {
 	Part2(io.Reader) string
 }
 
-var puzzles = []puzzle{
-	adventoc2024.Day1{},
-	adventoc2024.Day2{},
+var puzzles = map[string]puzzle{
+	"1": adventoc2024.Day1{},
+	"2": adventoc2024.Day2{},
+	"3": adventoc2024.Day3{},
 }
 
 func main() {
 	flag.Parse()
-	pi := 0
-	if i := flag.Arg(0); i != "" {
-		var err error
-		pi, err = strconv.Atoi(i)
-		if err != nil {
-			log.Fatalf("invalid puzzle day: %s", i)
-		}
-		pi--
-
-		if pi < 0 || pi > len(puzzles) {
-			log.Fatalf("puzzle index %d is out of range", pi)
-		}
+	puzzle, ok := puzzles[flag.Arg(0)]
+	if !ok {
+		log.Fatalf("invalid puzzle day %s", flag.Arg(0))
 	}
 
 	buf := new(bytes.Buffer)
 	tee := io.TeeReader(os.Stdin, buf)
 
-	puzzle := puzzles[pi]
-
 	fmt.Println("Part 1:", puzzle.Part1(tee))
 	fmt.Println("Part 2:", puzzle.Part2(buf))
 }