Buggy python submission (verdict: Runtime Error):

def submit():
    k = int(input())

    if k % 2 == 0:
        print(-1)
        return
    if k == 5:
        print(-1)
        return

    d = {}
    for t in [1, 3, 7, 9]:
        d[t] = {}
        for i in range(10):
            d[t][t * i % 10] = i
    
    td = k % 10
    curr = 0
    count = 0
    while count == 0 or curr != 0:
        diff = 7 - (curr % 10)
        if diff != 0:
            if diff < 0:
                diff += 10
            coef = d[td][diff]
            curr += coef * k
        curr //= 10
        count += 1

    print(count)
    

submit()    

Fixed submission:

def submit():
    k = int(input())

    if k % 2 == 0:
        print(-1)
        return
    if k % 5 == 0:
        print(-1)
        return

    d = {}
    for t in [1, 3, 7, 9]:
        d[t] = {}
        for i in range(10):
            d[t][t * i % 10] = i
    
    td = k % 10
    curr = 0
    count = 0
    while count == 0 or curr != 0:
        diff = 7 - (curr % 10)
        if diff != 0:
            if diff < 0:
                diff += 10
            coef = d[td][diff]
            curr += coef * k
        curr //= 10
        count += 1

    print(count)
    
submit()

Buggy python submission (verdict: Runtime Error):

def next7(s):
    return s * 10 + 7


def submit():
    k = int(input())

    if k % 2 == 0:
        print(-1)
        return
    if k == 5:
        print(-1)
        return

    d = {}
    for t in [1, 3, 7, 9]:
        d[t] = {}
        for i in range(10):
            d[t][t * i % 10] = i
    
    td = k % 10
    curr = 0
    digit = 1
    count = 0
    while count == 0 or curr != 0:
        diff = 7 - (curr % 10)
        if diff != 0:
            if diff < 0:
                diff += 10
            coef = d[td][diff]
            curr += coef * k
        curr //= 10
        count += 1

    print(count)
        


submit()    

Fixed submission:

def submit():
    k = int(input())

    if k % 2 == 0:
        print(-1)
        return
    if k % 5 == 0:
        print(-1)
        return

    d = {}
    for t in [1, 3, 7, 9]:
        d[t] = {}
        for i in range(10):
            d[t][t * i % 10] = i
    
    td = k % 10
    curr = 0
    count = 0
    while count == 0 or curr != 0:
        diff = 7 - (curr % 10)
        if diff != 0:
            if diff < 0:
                diff += 10
            coef = d[td][diff]
            curr += coef * k
        curr //= 10
        count += 1

    print(count)
    
submit()

Buggy python submission (verdict: Time Limit Exceeded):

def next7(s):
    return s * 10 + 7


def submit():
    k = int(input())

    if k % 2 == 0:
        print(-1)
        return
    if k == 5:
        print(-1)
        return

    s = 7
    ans = 1
    while s % k:
        s = next7(s)
        ans += 1

    print(ans)


submit()    

Fixed submission:

def submit():
    k = int(input())

    if k % 2 == 0:
        print(-1)
        return
    if k % 5 == 0:
        print(-1)
        return

    d = {}
    for t in [1, 3, 7, 9]:
        d[t] = {}
        for i in range(10):
            d[t][t * i % 10] = i
    
    td = k % 10
    curr = 0
    count = 0
    while count == 0 or curr != 0:
        diff = 7 - (curr % 10)
        if diff != 0:
            if diff < 0:
                diff += 10
            coef = d[td][diff]
            curr += coef * k
        curr //= 10
        count += 1

    print(count)
    
submit()

Buggy python submission (verdict: Time Limit Exceeded):

def next7(s):
    return s * 10 + 7


def submit():
    k = int(input())

    if k % 2 == 0:
        print(-1)
        return

    s = 7
    ans = 1
    while s % k:
        s = next7(s)
        ans += 1

    print(ans)


submit()    

Fixed submission:

def submit():
    k = int(input())

    if k % 2 == 0:
        print(-1)
        return
    if k % 5 == 0:
        print(-1)
        return

    d = {}
    for t in [1, 3, 7, 9]:
        d[t] = {}
        for i in range(10):
            d[t][t * i % 10] = i
    
    td = k % 10
    curr = 0
    count = 0
    while count == 0 or curr != 0:
        diff = 7 - (curr % 10)
        if diff != 0:
            if diff < 0:
                diff += 10
            coef = d[td][diff]
            curr += coef * k
        curr //= 10
        count += 1

    print(count)
    
submit()