Rust:codewars DNA to RNA conversion_rust

Algorithm
Dna_to_rna ("Gcat")//=> "Gcau"
The input character T is converted to u, or vice versa.

This question is very easy, but put here, mainly want to hint, rust has two kinds of solution of the pattern.

Non-replace mode:
1,

fn Dna_to_rna (DNA: &str)-> String {
  dna.chars (). Map (|c| match c {' T ' => ' U ', K => k}). Collect ()
}

2,

fn Dna_to_rna (DNA: &str)-> String {
  dna.split ("T") .collect::<vec<&str>> (). Join ("U")
}

3,

fn Dna_to_rna (DNA: &str)-> String {
    dna.chars ()
        . Into_iter ()
        . Map (|x| match x {
            ' T ' => return "U". to_string (),
            ' u ' => return ' T '. to_string (),
            _ => return x.to_string (),
        })
        .collect::< Vec<string>> ()
        . Concat ()

}

Replace mode

1,

fn Dna_to_rna (DNA: &str)-> String {
 dna.replace ("T", "U")
}

2,

fn Dna_to_rna (DNA: &str)-> String {
   str::replace (DNA, "T", "U"). To_string ()
}

3,

fn Dna_to_rna (DNA: &str)-> String {
  dna.to_string (). Replace ("T", "U")
}