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Leetcode 2806. Account Balance After Rounded Purchase

Problem Statement

You are given an integer representing the initial balance in a bank account. You need to implement a function that simulates a purchase. After a purchase, the balance will be reduced. However, due to some promotion, the purchase amount will be rounded to the nearest multiple of 10 before being subtracted from the account balance.

Write a function int calculateBalance(int balance, int purchaseAmount) that takes two integer arguments: the initial balance and the purchase amount. The function should return the remaining balance after subtracting the rounded purchase amount.

Clarifying Questions

1. What should happen if the purchase amount is greater than the balance?
   • Assume purchases are valid and will always be less than or equal to the balance for simplification.
2. How should we handle rounding of the purchase amount?
   • Round to the nearest multiple of 10:
     • Examples:
       • 5 rounds to 10
       • 13 rounds to 10
       • 25 rounds to 30
       • 27 rounds to 30
3. Will the purchase amount and balance always be positive integers?
   • For simplicity, yes, you can assume both are positive integers.

Code

#include <cmath>

int calculateBalance(int balance, int purchaseAmount) {
    // Round the purchaseAmount to the nearest multiple of 10.
    int roundedPurchase = round(purchaseAmount / 10.0) * 10;
    
    // Calculate the remaining balance.
    int remainingBalance = balance - roundedPurchase;
    
    return remainingBalance;
}

Strategy

1. Rounding:
   • Use the standard round function which rounds to the nearest integer.
   • To round to the nearest multiple of 10, divide the purchase amount by 10, round it, then multiply back by 10.
2. Subtract and Return:
   • Once the rounded value is determined, subtract it from the initial balance and return the result.

Time Complexity

• Time Complexity:
  • The time complexity for this operation is O(1). The calculations involved (division, rounding, multiplication, and subtraction) are all constant time operations.
• Space Complexity:
  • The space complexity is O(1) since we are using a constant amount of space to store intermediate variables.

Feel free to ask more questions or request further clarifications!

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