Move code out of cmd

day3/battery.go

@@ -0,0 +1,22 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+)
+
+func readBatteries(r io.Reader) (banks [][]uint8, err error) {
+	sc := bufio.NewScanner(r)
+	for sc.Scan() {
+		var bank []uint8
+		for _, b := range sc.Bytes() {
+			if b < '0' || b > '9' {
+				return nil, fmt.Errorf("bank %q: invalid joltage %q", sc.Text(), b)
+			}
+			bank = append(bank, b-'0')
+		}
+		banks = append(banks, bank)
+	}
+	return banks, sc.Err()
+}