# 1067. Digit Count in Range

• Time: $O(\log n)$
• Space: $O(1)$
  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 class Solution { public: int digitsCount(int d, int low, int high) { return countDigit(high, d) - countDigit(low - 1, d); } private: int countDigit(int n, int d) { int count = 0; for (int pow10 = 1; pow10 <= n; pow10 *= 10) { const int divisor = pow10 * 10; const int quotient = n / divisor; const int remainder = n % divisor; if (quotient > 0) count += quotient * pow10; if (d == 0) count -= pow10; if (remainder >= d * pow10) count += min(remainder - d * pow10 + 1, pow10); } return count; } }; 
  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 class Solution { public int digitsCount(int d, int low, int high) { return countDigit(high, d) - countDigit(low - 1, d); } private int countDigit(int n, int d) { int count = 0; for (int pow10 = 1; pow10 <= n; pow10 *= 10) { final int divisor = pow10 * 10; final int quotient = n / divisor; final int remainder = n % divisor; if (quotient > 0) count += quotient * pow10; if (d == 0) count -= pow10; if (remainder >= d * pow10) count += Math.min(remainder - d * pow10 + 1, pow10); } return count; } }