Problem:
Score : 500 points

Problem Statement

Find the number of integers between 1 and N (inclusive) that contains exactly K non-zero digits when written in base ten.

Constraints

1 \leq N < 10^{100}

1 \leq K \leq 3

Input

Input is given from Standard Input in the following format:

N
K

Output

Print the count.

Sample Input 1

100
1

Sample Output 1

19

The following 19 integers satisfy the condition:

1,2,3,4,5,6,7,8,9,10,20,30,40,50,60,70,80,90,100

Sample Input 2

25
2

Sample Output 2

14

The following 14 integers satisfy the condition:

11,12,13,14,15,16,17,18,19,21,22,23,24,25

Sample Input 3

314159
2

Sample Output 3

937

Sample Input 4

9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999
3

Sample Output 4

117879300

Solution in Rust (1.15.1) (judge verdict: Accepted)

// This code is generated by [cargo-atcoder](https://github.com/tanakh/cargo-atcoder)
// Original source code:
/*
use competitive::prelude::*;

fn main() {
    input! {
        n: Chars,
        kk: usize,
    }

    let n: Vec<u8> = n.into_iter().map(|c| c as u8 - '0' as u8).collect();

    let mut buf = vec![0; n.len()];
    let mut ans = 1;

    for b in 0..(10_usize).pow(kk as u32) {
        for i in 0..n.len() {
            buf[i] = (b % 10) as u8;
            if buf[i] == 0 {
                continue;
            }

            if kk == 1 {
                if buf <= n {
                    ans += 1;
                }
            } else {
                for j in i + 1..n.len() {
                    buf[j] = (b / 10 % 10) as u8;
                    if buf[j] == 0 {
                        continue;
                    }

                    if kk == 2 {
                        if buf <= n {
                            ans += 1;
                        }
                    } else {
                        for k in j + 1..n.len() {
                            buf[k] = (b / 100) as u8;
                            if buf[k] == 0 {
                                continue;
                            }

                            if buf <= n {
                                ans += 1;
                            }
                            buf[k] = 0;
                        }
                    }
                    buf[j] = 0;
                }
            }
            buf[i] = 0;
        }
    }
    ans -= 1;

    echo!(ans);
}
*/

fn main() {
    let exe = "/tmp/binC0FFCB62";
    std::io::Write::write_all(&mut std::fs::File::create(exe).unwrap(), &decode(BIN)).unwrap();
    std::fs::set_permissions(exe, std::os::unix::fs::PermissionsExt::from_mode(0o755)).unwrap();
    std::process::exit(std::process::Command::new(exe).status().unwrap().code().unwrap())
}

fn decode(v: &str) -> Vec<u8> {
    let mut ret = vec![];
    let mut buf = 0;
    let mut tbl = vec![64; 256];
    for i in 0..64 { tbl[TBL[i] as usize] = i as u8; }
    for (i, c) in v.bytes().filter_map(|c| { let c = tbl[c as usize]; if c < 64 { Some(c) } else { None } }).enumerate() {
        match i % 4 {
            0 => buf = c << 2,
            1 => { ret.push(buf | c >> 4); buf = c << 4; }
            2 => { ret.push(buf | c >> 2); buf = c << 6; }
            3 => ret.push(buf | c),
            _ => unreachable!(),
        }
    }
    ret
}

const TBL: &'static [u8] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
const BIN: &'static str = "<base64-encoded ELF executable removed>";