The facts are:
Given your friend's unfortunate taste preferences, you decide to split the bill only for non-spicy items. You will pay in full for the spicy dishes.
Given two ordered lists, one classifying the dishes as spicy vs. non-spicy and the other listing their prices, write a function that outputs a list where the first element is how much you pay and the second element is how much your friend pays.
bill_split(["S", "N", "S", "S"], [13, 18, 15, 4]) ➞ [41, 9]
# Since:
# You pay: [13, 9, 15, 4] = 41
# Friend pays: [0, 9, 0, 0] = 9
bill_split(["N", "S", "N"], [10, 10, 20]) ➞ [25, 15]
# You pay for half of both "N" dishes (5 + 10) and entirely pay for the "S" dish (10).
bill_split(["N", "N"], [10, 10]) ➞ [10, 10]
bill_split(["S", "N"], [41, 10]) ➞ [46, 5]
[your payment, friend's payment]N (you're not going to let your poor friend go hungry, are you?).