Number of Digit One LeetCode solution in C++

1
class Solution {
2
 public:
3
  int countDigitOne(int n) {
4
    int c = 0;
5
    for (int i = 1; i <= n; i++) {
6
      string s = to_string(i);
7
      c += count(s.begin(), s.end(), '1');
8
    }
9
    return c;
10
  }
11
};
12

13
// T.C. --> O(n * log(n))
14
// S.C. --> O(log(n))