are_concatable_strings.rs

fn are_concatable_strings(a: &str, b: &str, result: &str) -> bool {
    if a.len() + b.len() != result.len() {
        return false;
    }
    let a: Vec<_> = a.chars().collect();
    let b: Vec<_> = b.chars().collect();
    let result: Vec<_> = result.chars().collect();

    let mut i = 0;
    let mut j = 0;
    let mut k = 0;
    let mut match_len = 0;
    while k < result.len() {
        let ai = a.get(i);
        let bj = b.get(j);
        let ref rk = result[k];

        if ai == Some(rk) && bj == Some(rk) {
            match_len += 1;
            i += 1;
            j += 1;
            k += 1;
        } else if ai == Some(rk) {
            i += 1;
            j -= match_len;
            match_len = 0;
            k += 1;
        } else if bj == Some(rk) {
            j += 1;
            i -= match_len;
            match_len = 0;
            k += 1;
        } else if ai == None && bj == None || match_len != 0 {
            j -= match_len;
            match_len = 0;
        } else {
            return false;
        }
    }

    true
}

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

    macro_rules! generate_test {
        ($name:ident, $c:expr, $a:expr, $b:expr, $result:expr) =>  {
            #[test]
            fn $name() {
                assert_eq!(are_concatable_strings($a, $b, $c), $result);
            }
        }
    }

    generate_test!(a, "javascript", "javpt", "ascri", true);
    generate_test!(b, "javascript", "jasrit", "vacp", true);
    generate_test!(c, "javascript", "java", "scripts", false);
    generate_test!(d, "javascript", "jav", "script", false);
    generate_test!(e, "java not script", "java ", "not script", true);
    generate_test!(f, "javascript", "java ", "scritp", false);
    generate_test!(g, "Java1Java3Java2Java4", "Java2Java4", "Java1Java3", true);
    generate_test!(h, "jjaaamaaat", "jaaam", "jaaat", true);
    generate_test!(m, "jjbaaamqtba", "jaaam", "jbqtba", true);
}