// Incomplete
impl Solution {
    pub fn longest_valid_parentheses(s: String) -> i32 {
        if s.len() == 0 { 0 }
        let mut s = 0;
        let mut open = 0;
        let mut acc = 0;
        for c in s.chars().into_iter() {
            if c == '(' {
                open += 1;
            } else {
                open -= 1;
            }
            if open == 0 {

            }
        }
    }
}