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2180. Count Integers With Even Digit Sum 👍

  • Time: $O(\log \texttt{num})$
  • Space: $O(1)$
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class Solution {
 public:
  int countEven(int num) {
    return (num - sumOfDigit(num) % 2) / 2;
  }

 private:
  int sumOfDigit(int num) {
    int sum = 0;
    while (num) {
      sum += num % 10;
      num /= 10;
    }
    return sum;
  }
};

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class Solution {
  public int countEven(int num) {
    if (sumOfDigit(num) % 2 == 0)
      return num / 2;
    return (num - 1) / 2;
  }

  private int sumOfDigit(int num) {
    int sum = 0;
    while (num > 0) {
      sum += num % 10;
      num /= 10;
    }
    return sum;
  }
}

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class Solution:
  def countEven(self, num: int) -> int:
    return (num - self.sumOfDigit(num) % 2) // 2

  def sumOfDigit(self, num: int) -> int:
    summ = 0
    while num:
      summ += num % 10
      num //= 10
    return summ