Account Balance After Rounded Purchase — LeetCode 2806 Python Solution

The problem

Initially, you have a bank account balance of 100 dollars. You are given an integer purchaseAmount representing the amount you will spend on a purchase in dollars, in other words, its price.

Python solution

class Solution:
    def accountBalanceAfterPurchase(self, purchaseAmount: int) -> int:
        diff, x = 100, 0
        for y in range(100, -1, -10):
            if (t := abs(y - purchaseAmount)) < diff:
                diff = t
                x = y
        return 100 - x

Complexity

Pattern: Math and Number Theory

Find the closed form, the invariant, or the modular identity — and skip the loop entirely. LeetCode 2806. Account Balance After Rounded Purchase is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Math.

The math and number theory guide has the Python template for the pattern and the 485 LeetCode problems that use it.

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