LeetCode 678. Valid Parenthesis String

Problem Statement

impl Solution {
    fn check(s: &String, start: usize, c: i32) -> bool {
        let mut count = c;
        if count < 0 {
            return false;
        }

        for i in start..s.len() {
            let c = s.chars().nth(i).unwrap();
            if c == '(' {
                count += 1;
            } else if c == ')' {
                if count <= 0 {
                    return false;
                }
                count -= 1;
            } else if c == '*' {
                return Self::check(s, i + 1, count + 1) ||
                    Self::check(s, i + 1, count - 1) ||
                    Self::check(s, i + 1, count);
            }
        }
        return count == 0;
    }

    pub fn check_valid_string(s: String) -> bool {
        return Self::check(&s, 0, 0);
    }
}