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You are given a floating-point number amount representing the total amount of money you have, and you are making a purchase of some item which costs a floating-point amount purchase_cost. After the purchase, the remaining balance should be rounded to the nearest whole number. Implement a function that returns this remaining balance after the rounded purchase.

Clarifying Questions

  1. Q: Should the rounding be performed before or after subtracting the purchase cost from the total amount? A: The rounding should be executed after subtracting the purchase cost from the total amount.

  2. Q: How to handle edge cases where the subtraction results in a negative value? A: We should ensure that subtraction does not result in negative balance, typically by assuming transactions that result in negative balance are not allowed.

  3. Q: What about the precision of floating-point calculations? A: Python natively handles floating-point arithmetic with sufficient precision for this problem.

Strategy

  1. Subtract purchase_cost from amount to get the balance.
  2. Use Python’s built-in round function to round this balance to the nearest whole number.
  3. Return the rounded balance.

Code

def remaining_balance(amount: float, purchase_cost: float) -> int:
    # Calculate the remaining balance after the purchase
    balance = amount - purchase_cost
    # Round the balance to the nearest whole number
    rounded_balance = round(balance)
    return rounded_balance

Time Complexity

The time complexity is O(1) since the subtraction and rounding operations are constant time operations.

Example

# Example test cases

# Test case 1
amount = 100.50
purchase_cost = 25.75
print(remaining_balance(amount, purchase_cost)) # Expected output: 74

# Test case 2
amount = 50.0
purchase_cost = 19.99
print(remaining_balance(amount, purchase_cost)) # Expected output: 30

# Test case 3
amount = 10.0
purchase_cost = 10.0
print(remaining_balance(amount, purchase_cost)) # Expected output: 0

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