ValidParentheses.py

'''
Description:
Write a function called that takes a string of parentheses, and determines if the order of the parentheses is valid.
 The function should return true if the string is valid, and false if it's invalid.

Examples
"()"              =>  true
")(()))"          =>  false
"("               =>  false
"(())((()())())"  =>  true
Constraints
0 <= input.length <= 100

Along with opening (() and closing ()) parenthesis, input may contain any valid ASCII characters. 
Furthermore, the input string may be empty and/or not contain any parentheses at all.
 Do not treat other forms of brackets as parentheses (e.g. [], {}, <>).
'''

def valid_parentheses(string):
    a = 0
    for i in string:
        if a < 0:
            return False
        if i == '(':
            a +=1
        elif i == ')':
            a -= 1
    if a != 0:
        return False
    else:
        return True


print(valid_parentheses('hi())('))