## Codility : Nesting

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.

Assume that:

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

Complexity:

- expected worst-case time complexity is O(N);
- expected worst-case space complexity is O(1) (not counting the storage required for input arguments).

**PYTHON SOLUTION**

def solution(S):

# write your code in Python 2.7

if not S:

return 1

if len(S) ==1:

return 0

if S[0] ==")":

return 0

opens=[]

n=len(S)

for i in range(0,n):

if S[i] =="(":

opens.append(S[i])

elif S[i] ==")":

if len(opens) ==0:

return 0

elif "(" != opens.pop():

return 0

if len(opens) ==0:

return 1

return 0