301 Remove Invalid Parentheses

Remove the minimum number of invalid parentheses in order to make the input string valid. Return all possible results.

Note: The input string may contain letters other than the parentheses ( and ).

Examples:

"()())()" -> ["()()()", "(())()"]
"(a)())()" -> ["(a)()()", "(a())()"]
")(" -> [""]

Solution
屁都不会，心烦！

def helper(s, istart, i_delete, res, left, right):
  i, n = istart, len(s)
  count = 0
  for i in range(istart, n, 1):
    if ( s[i] == left ): count += 1
    if ( s[i] == right ): count -= 1
    if ( count != -1 ): continue
    for j in range(i_delete, i+1, 1):
      if ( s[j] == right and ( j == i_delete or s[j-1] != right) ):
        helper(s[0:j] + s[j+1:], i, j, res, left, right)
    return res
  if ( count == 0 ):
    if ( left == '(' ): res.append(s)
    else:
      s = s[::-1]
      res.append(s)
    return
  s = s[::-1]
  helper(s, 0, 0, res, ')', '(')
  return

class Solution(object):
    def removeInvalidParentheses(self, s):
        """
        :type s: str
        :rtype: List[str]
        """
        res = []
        helper(s, 0, 0, res, '(', ')')
        return res