I hate 67 (Editorial)

We've one of the conditions must hold :

• $6$ appears before $7$.

• $7$ appears before $6$.

observe that we can merge the two conditions by just checking if both $6$ and $7$ exists in the string $s$.

def solve():
    n=int(input())
    s=input()
    if('6' in s and '7' in s):
        print("NO")
    else:
        print("YES")

for _ in range(int(input())):
    solve()