Given a string, make every consonant after a vowel uppercase.

main.rs

fn main() {
    println!("{}", capitalize_post_vowels("Hello, World!".to_string()));
}

/// Given a string, make every consonant after a vowel uppercase.
fn capitalize_post_vowels(s: String) -> String {
    let mut prev = false;

    s.chars()
        .into_iter()
        .map(|c| match c {
            'a' | 'e' | 'i' | 'o' | 'u' | 'A' | 'E' | 'I' | 'O' | 'U' => {
                prev = true;
                c
            }
            c if c.is_ascii_alphabetic() => {
                let mut c = c;
                if prev {
                    c = c
                        .to_uppercase()
                        .to_string()
                        .chars()
                        .nth(0)
                        .expect("failed to convert to char");
                }
                prev = false;
                c
            }
            c => c,
        })
        .collect()
}

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

    #[test]
    fn test_capitalize_post_vowels() {
        assert_eq!(
            "heLlo WoRld".to_string(),
            capitalize_post_vowels("hello world".to_string())
        );
        assert_eq!(
            "xaaBeueKaDii".to_string(),
            capitalize_post_vowels("xaabeuekadii".to_string())
        );
    }
}