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 Java8 (OpenJDK 1.8.0) (judge verdict: Wrong Answer)

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.math.BigInteger;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.StringTokenizer;
import java.util.TreeMap;

public class Main {

	static class Task {

		int[] mapper = {0,2,5,5,4,5,6,3,7,6};
		Integer[] rankingArray = {1,7,4,2,3,5,9,6,8};
		ArrayList<Integer> ranking = new ArrayList<>(Arrays.asList(rankingArray));
		Integer[] rankingMapping = {-1,0,3,4,2,5,7,1,8,6};

		public void solve(InputReader in, PrintWriter out) {
			int n = in.nextInt();
			int m = in.nextInt();
			HashSet<Integer> nums = new HashSet<Integer>();
			for(int i=0; i<m; i++) {
				nums.add(in.nextInt());
			}

			for(int i=8; i>=0; i--) {
				if(!nums.contains(ranking.get(i)))
					ranking.remove(i);
			}

			BigInteger ans = use(n, BigInteger.ZERO, BigInteger.ONE);

			out.println(ans);
		}

		public BigInteger use(int sticks, BigInteger num, BigInteger factor) {
			BigInteger ans = BigInteger.ZERO;

			if(sticks == 0)
				return(num);
			if(sticks < 0)
				return(null);

			if(sticks >= 20) {
				int newSticks = sticks - mapper[ranking.get(0)];
				BigInteger newNum = num.add( BigInteger.valueOf(ranking.get(0)).multiply(factor) );
				BigInteger nextAns = use(newSticks, newNum, factor.multiply(BigInteger.valueOf(10)));
				if(nextAns != null)
					ans = ans.max(nextAns);
			} else {
				for(int i=0; i<ranking.size(); i++) {
					int newSticks = sticks - mapper[ranking.get(i)];
					BigInteger newNum = num.add( BigInteger.valueOf(ranking.get(i)).multiply(factor) );
					BigInteger nextAns = use(newSticks, newNum, factor.multiply(BigInteger.valueOf(10)));
					if(nextAns != null)
						ans = ans.max(nextAns);
				}
			}
			return ans;
		}
	}

	public static void main(String argds[]) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		InputReader in = new InputReader(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		Task solver = new Task();
		solver.solve(in, out);
		out.close();
	}

	static class InputReader {
		public BufferedReader reader;
		public StringTokenizer tokenizer;

		public InputReader(InputStream stream) {
			reader = new BufferedReader(new InputStreamReader(stream), 32768);
			tokenizer = null;
		}
		public String next() {
			while (tokenizer == null || !tokenizer.hasMoreTokens()) {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			}
			return tokenizer.nextToken();
		}

		public int nextInt() {
			return Integer.parseInt(next());
		}

		public long nextLong() {
			return Long.parseLong(next());
		}
	}	
}