Codility 7.3 Nesting

Determine whether a given string of parentheses (single type) is properly nested.

Task description
A string S consisting of N characters is called properly nested if:

S is empty;
S has the form "(U)" where U is a properly nested string;
S has the form "VW" where V and W are properly nested strings.
For example, string "(()(())())" is properly nested but string "())" isn't.

Write a function:

def solution(S)

that, given a string S consisting of N characters, returns 1 if string S is properly nested and 0 otherwise.

For example, given S = "(()(())())", the function should return 1 and given S = "())", the function should return 0, as explained above.

Write an efficient algorithm for the following assumptions:

N is an integer within the range [0..1,000,000];
string S consists only of the characters "(" and/or ")".

这题和7.1一个思路，而且花样没那么多。

def solution(S):
    # write your code in Python 3.6
    if len(S)%2 ==1:
        return 0
    stack = []
    for i in S:
        if i=="(":
            stack.append(i)        
        else:
            if len(stack)==0:
                return 0
            else:
                stack.pop()
                continue                
    if len(stack)==0:
        return 1
    else:
        return 0