Case permutations

case_permutations.rs

pub fn case_permutations(s: String) -> Vec<String> {
    let mut stack: Vec<String> = vec![String::with_capacity(s.capacity())];

    for c in s.chars() {
        if c.is_ascii_alphabetic() {
            let mut new_stack: Vec<String> = vec![];
            for p in stack {
                let mut lower = p.clone();
                lower.push(c.to_ascii_lowercase());
                new_stack.push(lower);

                let mut upper = p;
                upper.push(c.to_ascii_uppercase());
                new_stack.push(upper);
            }
            stack = new_stack;
        } else {
            for p in stack.iter_mut() {
                p.push(c);
            }
        }
    }

    stack
}

#[test]
fn test_case_permutations() {
    assert_eq!(
        case_permutations("ab2".to_string()),
        vec!["ab2", "aB2", "Ab2", "AB2"]
    );
    assert_eq!(case_permutations("35p".to_string()), vec!["35p", "35P"]);
}