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: Accepted)

use std::io::*;
use std::str::FromStr;
use std::cmp::*;

const need: [usize; 9] = [2,5,5,4,5,6,3,7,6];

fn func(dp: Vec<usize>, keta: usize, nokori: usize, vec: Vec<bool>) {
    if keta == 1 {
        for i in (0..9).rev() {
            if vec[i] && nokori == need[i] {
                print!("{}", i+1);
                return;
            }
        }
    }
    for i in (0..9).rev() {
        if vec[i] && nokori >= need[i] && keta-1 == dp[nokori - need[i]] {
            print!("{}", i+1);
            func(dp, keta-1, nokori - need[i], vec);
            return;
        }
    }
}

fn main() {
    let n: usize = read();
    let m: usize = read();
    let mut vec: Vec<bool> = vec![false; 9];
    for _ in 0..m {
        let a: usize = read();
        vec[a-1] = true;
    }
    let mut dp: Vec<usize> = vec![0; n+1];
    for i in 0..n {
        for j in 0..9 {
            if vec[j] && i+1 >= need[j] {
                let po = i+1 - need[j];
                if !(dp[po] == 0 && po != 0){
                    dp[i+1] = max(dp[i+1], dp[po] + 1);
                }
            }
        }
    }
    let maxk = dp[n];
    func(dp, maxk, n, vec);
    println!();
}

fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.unwrap() as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().unwrap()
}