Alternating digit sum

Math

69.0% acceptance

Feb 25, 2026

478

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. Each other digit has an opposite sign to its adjacent digits. Return the sum of all digits with their corresponding sign.

Solution

Rust

Time O(n)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn alternate_digit_sum(n: i32) -> i32 {
    let digits: Vec<i32> = {
      let mut v = Vec::new();
      let mut m = n;
      while m > 0 {
        v.push(m % 10);
        m /= 10;
      }
      v.reverse();
      v
    };
    digits
      .iter()
      .enumerate()
      .map(|(i, &d)| if i % 2 == 0 { d } else { -d })
      .sum()
  }
}