leetcode

0 class Solution {

1 public:

2 int countDigitOne(int n) const {

3 int res = 0;

4

5 for (long long m = 1; m <= n; m *= 10) {

6 const int a = n / m, b = n % m;

7 res += (a + 8) / 10 * m + (a % 10 == 1) * (b + 1);

8 }

9

10 return res;

11 }

12 };