Alternating Digit Sum — LeetCode 2544 Python Solution

The problem

You are given a positive integer n. Each digit of n has a sign according to the following rules: The most significant digit is assigned a positive sign.

Example

Input

n = 521

Output

4

Explanation

(+5) + (-2) + (+1) = 4.

Python solution

class Solution:
    def alternateDigitSum(self, n: int) -> int:
        return sum((-1) ** i * int(x) for i, x in enumerate(str(n)))

Complexity

Pattern: Math and Number Theory

Find the closed form, the invariant, or the modular identity — and skip the loop entirely. LeetCode 2544. Alternating Digit Sum 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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