This is yet another problem dealing with regular bracket sequences.

We should remind you that a bracket sequence is called regular, if by inserting «+» and «1» into it we can get a correct mathematical expression. For example, sequences «(())()», «()» and «(()(()))» are regular, while «)(», «(()» and «(()))(» are not. 

You are given a string of «(» and «)» characters. You are to find its longest substring that is a regular bracket sequence. You are to find the number of such substrings as well.
The first line of the input file contains a non-empty string, consisting of «(» and «)» characters. Its length does not exceed 10<sup class="upper-index">6</sup>.
class Solution:
    def longestValidParentheses(self, s: str) -> int:
        ans = [0, 1]
        stk = []
        

        for right, x in enumerate(s):
            if x == "(":
                stk.append(right)
            else:
                if stk and s[stk[-1]] == "(":
                    idx = stk.pop()
                    if stk:
                        t = right - stk[-1]
                    else:
                        t = right + 1
                    if t == ans[0]:
                        ans[1] += 1
                    elif t > ans[0]:
                        ans = [t, 1]
                else:
                    stk.append(right)
        
        return ans