balance parens

main.rs

/// Given a string of parenthesis, return the number of parenthesis you need to add to the string in order for it to be balanced.
///
/// Examples:
///
/// ```bash
/// > numBalanced(`()`)
/// > 0
///
/// > numBalanced(`(()`)
/// > 1
///
/// > numBalanced(`))()))))()`)
/// > 6
///
/// > numBalanced(`)))))`)
/// > 5
/// ```

fn main() {
    println!("{}", balance("))()))))()".to_string()));
}

fn balance(s: String) -> isize {
    let mut to_balance: isize = 0;

    for c in s.chars() {
        match c {
            '(' => to_balance += 1,
            ')' => to_balance -= 1,
            _ => unreachable!("unexpected character"),
        }
    }

    to_balance.abs()
}

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

    #[test]
    fn test_balance() {
        assert_eq!(0, balance("()".to_string()));
        assert_eq!(1, balance("(()".to_string()));
        assert_eq!(6, balance("))()))))()".to_string()));
        assert_eq!(5, balance(")))))".to_string()));
    }
}