pub struct Solution;
impl Solution {
    pub fn generate_parenthesis(n: i32) -> Vec<String> {
        let mut operations = vec![(0, 0, "".to_string())];
        let mut result = vec![];
        while let Some((left, right, s)) = operations.pop() {
            if s.len() == n as usize * 2 {
                result.push(s);
                continue;
            }
            if left < n { operations.push((left + 1, right, s.clone() + "(")); }
            if right < left { operations.push((left, right + 1, s + ")")); }
        }
        return result;
    }
}

#[cfg(test)]
mod tests {
    use super::Solution;

    #[test]
    fn test1() {
        let mut actual = Solution::generate_parenthesis(3);
        actual.sort();
        assert_eq!(actual, vec!["((()))","(()())","(())()","()(())","()()()"]);
    }

    #[test]
    fn test2() {
        assert_eq!(Solution::generate_parenthesis(1), vec!["()"]);
    }
}