Count Decimal One Digits up to a Bound
Company: Google
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: hard
Interview Round: Other
### Problem
Count all appearances of decimal digit 1 in the ordinary spellings of integers from 0 through n, inclusive. Count occurrences, not merely how many numbers contain a 1.
```cpp
int countDigitOne(int n);
```
### Examples
```text
n = 20 -> 12
n = 101 -> 23
```
### Constraints
- 0 <= n <= 1000000000.
Overview: Count Decimal One Digits up to a Bound. Count all appearances of decimal digit 1 in the ordinary spellings of integers from 0 through n, inclusive. Count occurrences, not merely how many numbers conta