remove invalid parentheses

 1def removeInvalidParentheses(s):
 2    def isvalid(s):
 3        ctr = 0
 4        for c in s:
 5            ctr += (c == "(") - (c == ")")
 6            if ctr < 0:
 7                return False
 8        return ctr == 0
 9
10    level = {s}
11    while True:
12        valid = [*filter(isvalid, level)]
13        if valid:
14            return valid
15        level = {s[:i] + s[i + 1 :] for s in level for i in range(len(s))}
16
17
18r = removeInvalidParentheses("(a)())()")
19print(r)
20
21["(a)()()", "(a())()"]