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 C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;
using System.Linq;
 
public class Program
{
	public static void Main()
	{
		var rule = new int[]{2,5,5,4,5,6,3,7,6};
		var split = Console.ReadLine().Split().Select(int.Parse).ToList();
		var n = split[0];
		var m = split[1];
		split = Console.ReadLine().Split().Select(int.Parse).ToList();
		Check(split);
		var rule2 = new Dictionary<int,int>();
		var rule_list = new Dictionary<int,List<int>>();
		foreach(var v in split){
			rule2.Add(rule[v-1],v);
			rule_list.Add(rule[v-1],new List<int>{v});
		}
		var min = rule2.Keys.Min();
		var max = n/min;
		if(min*max == n){
			for(int i = 0;i<max;i++){
				Console.Write(rule2[min]);
			}
			Console.WriteLine();
		}
		else {
			var ans = Enumerable.Repeat(rule2[min], max).ToList();
			var plus = new List<Plus>();
			n = n % min;
			var count = 0;
			while(true){
				count++;
				var next_list = new Dictionary<int,List<int>>();
				foreach(var v in rule_list){
					foreach(var v2 in rule2){
						var tmp = new List<int>(v.Value);
						tmp.Add(v2.Value);
						if(rule_list.Keys.Contains(v2.Key+v.Key) || next_list.Keys.Contains(v2.Key+v.Key))continue;
						next_list.Add(v2.Key+v.Key,tmp);
					}
				}
				foreach(var v in next_list)rule_list.Add(v.Key,v.Value);
				if(rule2.Keys.Contains(n)){
					ans.Add(rule2[n]);
					PrintAns(ans);
					break;
				}
				else if(plus.Where(x=>x.k == n).Count()>0){
					var p = plus.Where(x=>x.k == n).ElementAt(0);
					foreach(var v in p.arr)ans.Add(v);
					PrintAns(ans);
					break;
				}
				ans.Remove(rule2[min]);
				n = n + min;
			}
		}
	}
	public static void Check(List<int> list){
		if(list.Contains(2)&&list.Contains(3)){
			list.Remove(2);
		}
		if(list.Contains(3)&&list.Contains(5)){
			list.Remove(3);
		}
		if(list.Contains(2)&&list.Contains(5)){
			list.Remove(2);
		}
		if(list.Contains(6)&&list.Contains(9)){
			list.Remove(6);
		}
	}
	public static void PrintAns(List<int> ans){
		ans.Sort((a,b)=>(int)b-(int)a);
		foreach(var v in ans){
			Console.Write(v);
		}
		Console.WriteLine();
	}
}
class Plus{
	public int[] arr;
	public int k;
	public Plus(int[] arr,int k){
		this.arr = arr;
		this.k = k;
	}
}