In Python, I cannot find a solution as to how to determine whether there is always a 0 following a 1 somewhere in a list of numbers, to form a pair 10. It doesn't have to be direct follower.

For clarity, I mean "list" as in (sort of) binary number, to be specific,

1100  #pass
1001  #fail
1010  #pass
0101  #fail11110000  #pass
11100001  #fail11100100  #pass

There must be always an equal number of 1es before 0es. Thanks in advance.

Keep a temp variable, initialized at 0. Increment it for each 1, decrement it otherwise. It should never be negative, and to make sure there are as many 1 as 0, it should be equal to 0 at the end.

def check(bits):temp = 0for bit in bits:if temp < 0:return Falseif int(bit) == 1:temp += 1else:temp -= 1return temp == 0

As an example:

>>> check('1100')
True
>>> check('110001')
False
>>> check('1')
False
>>> check('10')
True
>>> check('1010')
True
>>> check('123')
False