Problem:
Score : 400 points

Problem Statement

Find the largest integer that can be formed with exactly N matchsticks, under the following conditions:

Every digit in the integer must be one of the digits A_1, A_2, ..., A_M (1 \leq A_i \leq 9).

The number of matchsticks used to form digits 1, 2, 3, 4, 5, 6, 7, 8, 9 should be 2, 5, 5, 4, 5, 6, 3, 7, 6, respectively.

Constraints

All values in input are integers.

2 \leq N \leq 10^4

1 \leq M \leq 9

1 \leq A_i \leq 9

A_i are all different.

There exists an integer that can be formed by exactly N matchsticks under the conditions.

Input

Input is given from Standard Input in the following format:

N M
A_1 A_2 ... A_M

Output

Print the largest integer that can be formed with exactly N matchsticks under the conditions in the problem statement.

Sample Input 1

20 4
3 7 8 4

Sample Output 1

777773

The integer 777773 can be formed with 3 + 3 + 3 + 3 + 3 + 5 = 20 matchsticks, and this is the largest integer that can be formed by 20 matchsticks under the conditions.

Sample Input 2

101 9
9 8 7 6 5 4 3 2 1

Sample Output 2

71111111111111111111111111111111111111111111111111

The output may not fit into a 64-bit integer type.

Sample Input 3

15 3
5 4 6

Sample Output 3

654

Solution in Rust (1.15.1) (judge verdict: Runtime Error)

use std::cmp;

const C: [usize; 10] = [0, 2, 5, 5, 4, 5, 6, 3, 7, 6];

fn main() {
    let (r, w) = (std::io::stdin(), std::io::stdout());
    let mut sc = IO::new(r.lock(), w.lock());

    let n: usize = sc.read();
    let m: usize = sc.read();
    let a: Vec<usize> = sc.vec(m);
    let mut dp = vec![0; 30];

    for i in 0..dp.len() {
        if i > 0 && dp[i] == 0 {
            continue;
        }
        for &a in a.iter() {
            let cost = C[a];
            let a = a as i64;
            if i + cost >= dp.len() {
                continue;
            }
            dp[i + cost] = cmp::max(dp[i + cost], dp[i] * 10 + a);
        }
    }

    let mut candidate = vec![];
    for &a in a.iter() {
        let cost = C[a];
        let d = n / cost;
        for i in 0..cmp::min(16, d + 1) {
            let suffix = d - i;
            let remain = n % d + i * cost;
            if remain >= dp.len() {
                continue;
            }
            let max = dp[remain];
            if remain > 0 && max == 0 {
                continue;
            }
            candidate.push((suffix, a, max));
        }
    }

    let mut ans = candidate
        .into_iter()
        .flat_map(|(suffix, a, max)| {
            let mut r = vec![];

            let mut s = String::new();
            for _ in 0..suffix {
                s.push((a as u8 + '0' as u8) as char);
            }
            if max > 0 {
                s.push_str(max.to_string().as_str());
            }
            r.push(s);

            if max > 0 {
                let mut t = max.to_string();
                for _ in 0..suffix {
                    t.push((a as u8 + '0' as u8) as char);
                }
                r.push(t);
            }
            r
        })
        .collect::<Vec<_>>();
    ans.sort_by(|a, b| {
        let t = a.len().cmp(&b.len());
        if t == std::cmp::Ordering::Equal {
            a.cmp(&b)
        } else {
            t
        }
    });

    let ans = &ans[ans.len() - 1];
    println!("{}", ans);
}

pub struct IO<R, W: std::io::Write>(R, std::io::BufWriter<W>);

impl<R: std::io::Read, W: std::io::Write> IO<R, W> {
    pub fn new(r: R, w: W) -> IO<R, W> {
        IO(r, std::io::BufWriter::new(w))
    }
    pub fn write<S: std::ops::Deref<Target = str>>(&mut self, s: S) {
        use std::io::Write;
        self.1.write(s.as_bytes()).unwrap();
    }
    pub fn read<T: std::str::FromStr>(&mut self) -> T {
        use std::io::Read;
        let buf = self
            .0
            .by_ref()
            .bytes()
            .map(|b| b.unwrap())
            .skip_while(|&b| b == b' ' || b == b'\n' || b == b'\r' || b == b'\t')
            .take_while(|&b| b != b' ' && b != b'\n' && b != b'\r' && b != b'\t')
            .collect::<Vec<_>>();
        unsafe { std::str::from_utf8_unchecked(&buf) }
            .parse()
            .ok()
            .expect("Parse error.")
    }
    pub fn vec<T: std::str::FromStr>(&mut self, n: usize) -> Vec<T> {
        (0..n).map(|_| self.read()).collect()
    }
    pub fn chars(&mut self) -> Vec<char> {
        self.read::<String>().chars().collect()
    }
}