https://twitter.com/coproduto/status/1782352142050775113

balanced.rs

pub fn is_balanced(s: &str) -> bool {
    let mut stack = Vec::new();

    for c in s.chars() {
        match c {
            '(' | '[' | '{' => stack.push(c),
            symbol @ (')' | ']' | '}') if stack.pop() != reverse(symbol) => return false,
            _ => (),
        }
    }

    stack.is_empty()
}

fn reverse(c: char) -> Option<char> {
    Some(match c {
        ')' => '(',
        ']' => '[',
        '}' => '{',
        _ => c,
    })
}

Tests:

#[cfg(test)]
mod tests {
    #[test]
    fn test_is_balanced() {
        assert_eq!(super::is_balanced("abcd"), true);
        assert_eq!(super::is_balanced("(abcd)"), true);
        assert_eq!(super::is_balanced("(abcd"), false);
        assert_eq!(super::is_balanced("abcd]"), false);
        assert_eq!(super::is_balanced("(abc)d"), true);
        assert_eq!(super::is_balanced("(abc]d"), false);
        assert_eq!(super::is_balanced("(abc[%def])"), true);
        assert_eq!(super::is_balanced("$(abc[de]fg{hi}jk)%//"), true);
        assert_eq!(super::is_balanced("(({abc})"), false);
    }
}