extern crate rand;

trait Balanced {
    /// Returns true if the brackets are balanced
    fn is_balanced(&self) -> bool;
}

impl<'a> Balanced for str {
    fn is_balanced(&self) -> bool {
        let mut count = 0;

        for bracket in self.chars() {
            let change = match bracket {
                '[' => 1,
                ']' => -1,
                _ => panic!("Strings should only contain brackets")
            };

            count += change;
            if count < 0 { return false; }
        }

        count == 0
    }
}

/// Generates random brackets
fn generate_brackets(num: usize) -> String {
    use rand::random;

    (0..num).map(|_| if random() { '[' } else { ']' }).collect()
}

fn main() {
    for i in (0..10) {
        let brackets = generate_brackets(i);

        println!("{}    {}", brackets, brackets.is_balanced())
    }
}