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.Text;

namespace AtTest.ABC118
{
    class D
    {
        static void Main(string[] args)
        {
            Method(args);
            Console.ReadLine();
        }

        static void Method(string[] args)
        {
            int[] nm = ReadInts();
            int n = nm[0];
            int m = nm[1];
            int[] array = ReadInts();
            Array.Sort(array);
            //for (int i = 0; i < m; i++) Console.WriteLine(array[i]);
            //Array.Reverse(array);
            int[] costs = new int[9] { 2, 5, 5, 4, 5, 6, 3, 7, 6 };
            /*var dict = new Dictionary<int, char>();//cost,val
            for (int i = 0; i < array.Length; i++)
            {
                if (!dict.ContainsKey(costs[array[i] - 1]))
                {
                    dict.Add(costs[array[i] - 1], (char)('0' + array[i]));
                }
            }
            foreach (int key in dict.Keys)
                Console.WriteLine(key + " " + dict[key]);
                */
            string[] dp = new string[n + 10];
            for (int i = 0; i < dp.Length; i++) dp[i] = "";
            for (int i = 0; i < n; i++)
            {
                if (i > 0 && dp[i].Length == 0) continue;

                int val = 0;
                for (int j = Math.Max(0, dp[i].Length - 3); j < dp[i].Length; j++)
                {
                    val = val * 10 + dp[i][dp[i].Length - j - 1] - '0';
                }
                for (int j = 0; j < m; j++)
                {
                    int tmp = val * 10 + array[j];
                    int next = 0;
                    for (int k = Math.Max(0, dp[i+costs[array[j] - 1]].Length - 4) ;k< dp[i + costs[array[j] - 1]].Length; k++)
                    {
                        next = next*10
                            + dp[i + costs[array[j] - 1]][k] - '0';
                    }
                    if (dp[i].Length + 1 > dp[i + costs[array[j]-1]].Length
                        ||(dp[i].Length+1==dp[i + costs[array[j] - 1]].Length
                        &&tmp>next))
                    {
                        dp[i + costs[array[j] - 1]] = dp[i] + (char)(array[j] + '0');
                        //Console.WriteLine("updated");
                    }
                    //Console.WriteLine(tmp + " " + next + " "+dp[i].Length+" "+ dp[i + costs[array[j] - 1]].Length);
                }
            }
            //for (int i = 0; i <= n; i++) Console.WriteLine(dp[i]);
            Console.WriteLine(dp[n]);
        }

        private static string Read() { return Console.ReadLine(); }
        private static int ReadInt() { return int.Parse(Read()); }
        private static long ReadLong() { return long.Parse(Read()); }
        private static double ReadDouble() { return double.Parse(Read()); }
        private static int[] ReadInts() { return Array.ConvertAll(Read().Split(), int.Parse); }
        private static long[] ReadLongs() { return Array.ConvertAll(Read().Split(), long.Parse); }
        private static double[] ReadDoubles() { return Array.ConvertAll(Read().Split(), double.Parse); }
    }
}