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2544. Alternating Digit Sum 👍

  • Time: $O(\log n)$
  • Space: $O(1)$
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class Solution {
 public:
  int alternateDigitSum(int n) {
    int ans = 0;
    int sign = 1;

    for (; n > 0; n /= 10) {
      sign *= -1;
      ans += sign * n % 10;
    }

    return sign * ans;
  }
};

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class Solution {
  public int alternateDigitSum(int n) {
    int ans = 0;
    int sign = 1;

    for (; n > 0; n /= 10) {
      sign *= -1;
      ans += sign * n % 10;
    }

    return sign * ans;
  }
}

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class Solution:
  def alternateDigitSum(self, n: int) -> int:
    ans = 0
    sign = 1

    while n > 0:
      sign *= -1
      ans += n % 10 * sign
      n //= 10

    return sign * ans