Buggy python submission (verdict: Runtime Error):
N, M = [int(a) for a in input().split(" ")]
ctab = {"1":2,"2":5,"3":5,"4":4,"5":5,"6":6,"7":3,"8":7,"9":6}
A = [(a, ctab[a]) for a in input().split(" ")]
prev, curr = ([None]*(N+1), [None]*(N+1))
for char, cost in A:
    if not prev[cost] or char>prev[cost]:
        prev[cost] = char
ans = ""
while any(prev):
    for i in range(1, N+1):
        curr[i] = None
    for i in range(1, N+1):
        s = prev[i]
        if not s:
            continue
        for char, cost in A:
            if i+cost <= N:
                tmps = char+s
                if not curr[i+cost] or tmps > curr[i+cost]:
                    curr[i+cost] = tmps
    if curr[N] is not None:
        ans = curr[N]
    curr, prev = prev, curr
print(ans)

Fixed submission:
N, M = [int(a) for a in input().split(" ")]
ctab = {"1":2,"2":5,"3":5,"4":4,"5":5,"6":6,"7":3,"8":7,"9":6}
A = sorted([(a, ctab[a]) for a in input().split(" ")], key=lambda t:t[0])
prev, curr = ([""]*(N+1), [""]*(N+1))

def maxs(s1, s2):
    return max(s1, s2, key=lambda s:len(s)) if len(s1)!=len(s2) else max(s1,s2)

char, cost = A[0]
for i in range(1, N+1):
    d, r = divmod(i, cost)
    prev[i] = char*d if r==0 else None
for char, cost in A[1:]:
    for i in range(1, N+1):
        if i-cost >= 0 and curr[i-cost] is not None:
            tmp = char+curr[i-cost]
            curr[i] = maxs(tmp, prev[i]) if prev[i] else tmp
        else:
            curr[i] = prev[i]
    curr, prev = prev, curr
print(prev[-1])

Buggy python submission (verdict: Runtime Error):
N, M = [int(a) for a in input().split(" ")]
ctab = {"1":2,"2":5,"3":5,"4":4,"5":5,"6":6,"7":3,"8":7,"9":6}
A = [(a, ctab[a]) for a in input().split(" ")]
prev = [None]*(N+1)
curr = [None]*(N+1)
for char, cost in A:
    if not prev[cost] or char>prev[cost]:
        prev[cost] = char

ans = ""
while any(prev):
    for i in range(1, N+1):
        curr[i] = None
    for i in range(1, N+1):
        s = prev[i]
        if not s:
            continue
        for char, cost in A:
            tmps = char+s
            if i+cost <= N:
                if not curr[i+cost] or tmps > curr[i+cost]:
                    curr[i+cost] = tmps
    if curr[N] is not None:
        ans = curr[N]
    curr, prev = prev, curr
print(ans)


Fixed submission:
N, M = [int(a) for a in input().split(" ")]
ctab = {"1":2,"2":5,"3":5,"4":4,"5":5,"6":6,"7":3,"8":7,"9":6}
A = sorted([(a, ctab[a]) for a in input().split(" ")], key=lambda t:t[0])
prev, curr = ([""]*(N+1), [""]*(N+1))

def maxs(s1, s2):
    return max(s1, s2, key=lambda s:len(s)) if len(s1)!=len(s2) else max(s1,s2)

char, cost = A[0]
for i in range(1, N+1):
    d, r = divmod(i, cost)
    prev[i] = char*d if r==0 else None
for char, cost in A[1:]:
    for i in range(1, N+1):
        if i-cost >= 0 and curr[i-cost] is not None:
            tmp = char+curr[i-cost]
            curr[i] = maxs(tmp, prev[i]) if prev[i] else tmp
        else:
            curr[i] = prev[i]
    curr, prev = prev, curr
print(prev[-1])

Buggy python submission (verdict: Runtime Error):
from bisect import insort_left
N, M = [int(a) for a in input().split(" ")]
ctab = {"1":2,"2":5,"3":5,"4":4,"5":5,"6":6,"7":3,"8":7,"9":6}
A = [(a, ctab[a]) for a in input().split(" ")]
prev = [None]*(N+1)
curr = [None]*(N+1)
for char, cost in A:
    if not prev[cost] or char>prev[cost]:
        prev[cost] = char

def insert(s, char):
    ls = list(s)[::-1]
    insort_left(ls, char)
    return int("".join(ls[::-1]))

tmp = ""
while any(prev):
    for i in range(1, N+1):
        maxval = -1
        for char, cost in A:
            if i-cost>=0 and prev[i-cost]:
                val = insert(prev[i-cost], char)
                maxval = val if val > maxval else maxval
        curr[i] = str(maxval) if maxval > 0 else None
    if curr[N] is not None:
        tmp = curr[N]
    curr, prev = prev, curr
print(tmp)

Fixed submission:
N, M = [int(a) for a in input().split(" ")]
ctab = {"1":2,"2":5,"3":5,"4":4,"5":5,"6":6,"7":3,"8":7,"9":6}
A = sorted([(a, ctab[a]) for a in input().split(" ")], key=lambda t:t[0])
prev, curr = ([""]*(N+1), [""]*(N+1))

def maxs(s1, s2):
    return max(s1, s2, key=lambda s:len(s)) if len(s1)!=len(s2) else max(s1,s2)

char, cost = A[0]
for i in range(1, N+1):
    d, r = divmod(i, cost)
    prev[i] = char*d if r==0 else None
for char, cost in A[1:]:
    for i in range(1, N+1):
        if i-cost >= 0 and curr[i-cost] is not None:
            tmp = char+curr[i-cost]
            curr[i] = maxs(tmp, prev[i]) if prev[i] else tmp
        else:
            curr[i] = prev[i]
    curr, prev = prev, curr
print(prev[-1])