Get the number of ones in all positive integers less than or equal to N

main.rs

fn main() {
    println!("{}", number_of_ones(14));
}

/// Given an integer n, count the total number of 1 digits appearing in all non-negative integers less than or equal to n.
///
/// Example:
///
/// ```bash
/// > numberOfOnes(14)
/// > 7 // 1, 10, 11, 12, 13, 14
/// ```
fn number_of_ones(n: usize) -> usize {
    let mut o = 0;
    for i in 1..n + 1 {
        o += ones(i);
    }
    o
}

fn ones(mut n: usize) -> usize {
    let mut ones = 0;
    while n > 0 {
        let digit = n % 10;
        n = n / 10;

        if digit == 1 {
            ones += 1;
        }
    }
    ones
}