Python クラス用のクレジット カード支払い計算機を作成しています。課題は、x か月後に残高をゼロにするために必要な毎月の支払いを計算する計算機の定義を作成することです。
この定義には、initialBalance、apr、months の 3 つのパラメーターがあります。
私が理解できる限り、割り当てのポイントは、二分法を使用して答えを見つけることです。割り当てを支援する他の2つの定義を書きました。
1) newBalance() - 支払いが行われた後の新しい残高を決定します。2) balances() - 支払いが行われた後に残高のリストを返します。
その観点から、balances()[-1] は最終的な残高を返すので、私の行動計画は、リストの最後の項目を 0 に等しい (または少なくとも 0 の 0.005 以内!) と評価し、そうであれば返すことでした。私をそこに連れて行った支払い。
最終残高がマイナスの場合 (支払いすぎた!): payment = payment - (payment / 2); 残高がプラスの場合 (十分な支払いがありません!): payment = payment + (payment / 2);
私が理解できる限り、私のアルゴリズムは最終的に結論を出すはずですが、十分に近い答えを見つけることは決してありません...
これが私のコードです（そして最後に教授のテスト定義があります）：
def newBalance(prevBalance, apr, payment):
"""
- prevBalance: the balance on the credit card statement.
- apr: the annual percentage rate (15.9 here means 15.9%).
- payment: the amount paid this month to the credit card company.
- returns: the new balance that will be owed on the credit card
(assumes no purchases are made).
"""
interestCharge = float(((apr / 12.0) / 100) * prevBalance)
return float((interestCharge + prevBalance) - payment)
def balances(initialBalance, apr, payments):
"""
- initialBalance: the initial balance on the credit card.
- apr: the annual percentage rate (15.9 here means 15.9%).
- payments: a list of monthly payments made on the credit card.
- returns: a list giving the balance on the credit card each
month. The first number in the list is the initial
balance, the next number is the balance after the first
payment is made, and so on. Note that the length of the returned
list is len(payments) + 1.
"""
balancelist = []
balancelist.append(initialBalance)
for x in range(0, len(payments)):
balancelist.append(newBalance(balancelist[x], apr, payments[x]))
return balancelist
def findMonthlyPayment(initialBalance, apr, months):
"""
- initialBalance: the starting balance on the card.
- apr: the APR.
- months: the number of equal monthly payments you wish to
make in order to reduce the balance to zero.
- returns: the monthly payment amount needed to reduce the
balance to zero (well, "zero" to within $0.005, anyway)
in the given number of months.
"""
guess = float(initialBalance / months)
listo = months*[guess]
while True:
if abs(float(balances(initialBalance, apr, listo)[-1]) - initialBalance) < 0.006:
print "BINGO", guess ##for debugging
print balances(initialBalance, apr, listo)[-1]
return guess
else:
if float(balances(initialBalance, apr, listo)[-1]) < -0.005:
guess = guess - (guess / 2)
print "BOO", guess ##for debugging
print balances(initialBalance, apr, listo)[-1]
else:
guess = guess + (guess / 2)
print "NAY", guess ##for debugging
print balances(initialBalance, apr, listo)[-1]
listo = months*[guess]
def testFindMonthlyPayment():
answer = findMonthlyPayment(1000, 18.9, 60)
print
myString = "Monthly payment to pay off $%.2f in %d months at %.2f%% APR:"
print myString % (1000, 60, 18.9)
print "$%.2f" % answer
# Output should look approximately like this:
"""
iteration: 1 guess: 500.0 final bal: -46777.3384635
iteration: 2 guess: 250.0 final balance: -22111.7016729
iteration: 3 guess: 125.0 final balance: -9778.88327752
iteration: 4 guess: 62.5 final balance: -3612.47407985
iteration: 5 guess: 31.25 final balance: -529.269481021
iteration: 6 guess: 15.625 final balance: 1012.3328184
iteration: 7 guess: 23.4375 final balance: 241.531668687
iteration: 8 guess: 27.34375 final balance: -143.868906167
iteration: 9 guess: 25.390625 final balance: 48.83138126
iteration: 10 guess: 26.3671875 final balance: -47.5187624535
iteration: 11 guess: 25.87890625 final balance: 0.656309403241
iteration: 12 guess: 26.123046875 final balance: -23.4312265251
iteration: 13 guess: 26.0009765625 final balance: -11.387458561
iteration: 14 guess: 25.9399414062 final balance: -5.36557457885
iteration: 15 guess: 25.9094238281 final balance: -2.35463258781
iteration: 16 guess: 25.8941650391 final balance: -0.849161592282
iteration: 17 guess: 25.8865356445 final balance: -0.0964260945206
iteration: 18 guess: 25.8827209473 final balance: 0.27994165436
iteration: 19 guess: 25.8846282959 final balance: 0.0917577799204
iteration: 20 guess: 25.8855819702 final balance: -0.00233415730086
Monthly payment to pay off $1000.00 in 60 months at 18.90 APR:
$25.89
"""
助けてくれてありがとう。私が今までグーグルで検索したすべてがstackoverflowにない限り、おそらくcompsciに参加しなかったでしょう。