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()
}