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 Go (1.6) (judge verdict: Accepted)

package main

import (
	"bufio"
	"fmt"
	"io"
	"os"
	"sort"
	"strconv"
)

var (
	readString func() string
	stdout     *bufio.Writer
)

func init() {
	readString = newReadString(os.Stdin)
	stdout = bufio.NewWriter(os.Stdout)
}

func newReadString(ior io.Reader) func() string {
	r := bufio.NewScanner(ior)
	r.Buffer(make([]byte, 1024), int(1e+11))
	r.Split(bufio.ScanWords)

	return func() string {
		if !r.Scan() {
			panic("Scan failed")
		}
		return r.Text()
	}
}

func readInt() int {
	return int(readInt64())
}

func readInt64() int64 {
	i, err := strconv.ParseInt(readString(), 0, 64)
	if err != nil {
		panic(err.Error())
	}
	return i
}

func readIntSlice(n int) []int {
	b := make([]int, n)
	for i := 0; i < n; i++ {
		b[i] = readInt()
	}
	return b
}

func readLengthAndSlice() (int, []int) {
	n := readInt()
	return n, readIntSlice(n)
}

func printf(f string, args ...interface{}) (int, error) {
	return fmt.Fprintf(stdout, f, args...)
}

func println(args ...interface{}) (int, error) {
	return fmt.Fprintln(stdout, args...)
}

func eprintln(args ...interface{}) (int, error) {
	return fmt.Fprintln(os.Stderr, args...)
}

// readString() string
// readInt() int
// readIntSlice(n int) []int
// readLengthAndSlice() []int

// -----------------------------------------------------------------------------

var score []int = []int{0, 2, 5, 5, 4, 5, 6, 3, 7, 6}

type sortTarget0Slice []int

func (s sortTarget0Slice) Len() int {
	return len(s)
}

func (s sortTarget0Slice) Less(i, j int) bool {
	if score[s[i]] < score[s[j]] {
		return true
	} else if score[s[i]] > score[s[j]] {
		return false
	}
	return s[i] > s[j]
}

func (s sortTarget0Slice) Swap(i, j int) {
	s[i], s[j] = s[j], s[i]
}

func less(a, b string) bool {
	if len(a) < len(b) {
		return true
	} else if len(a) > len(b) {
		return false
	}
	av, _ := strconv.ParseInt(a[:1], 0, 64)
	bv, _ := strconv.ParseInt(b[:1], 0, 64)
	if av < bv {
		return true
	} else if av > bv {
		return false
	}
	return less(a[1:], b[1:])
}

func main() {
	defer stdout.Flush()
	n := readInt()

	m := readInt()
	a := make([]int, m)
	for i := range a {
		a[i] = readInt()
	}
	sort.Sort(sortTarget0Slice(a))

	dp := make([]string, n+1)
	for i := range dp {
		dp[i] = "_"
	}
	dp[0] = ""
	for i := 1; i <= n; i++ {
		for _, x := range a {
			p := i - score[x]
			if p < 0 || dp[p] == "_" {
				continue
			}
			s := fmt.Sprintf("%d%s", x, dp[p])
			if dp[i] == "_" || less(dp[i], s) {
				dp[i] = s
			}
		}
	}
	println(dp[n])
}

// -----------------------------------------------------------------------------