9: Improve solution for Rust track exercise "Raindrops".

Dependencies

• [2] MBAFQOWX 8: Improve solution for Rust track exercise "Raindrops".
• [3] N3POGH26 7: Add solution for Rust track exercise "Raindrops".
• [4] MSFESBT6 6: Add Rust track exercise "Raindrops".

Change contents

• replacement in rust/raindrops/src/lib.rs at line 2
  [3.1819]→[2.0:50](∅→∅)
  − let (a, b, mut c) = ("Pl", "ng", String::new());
  [3.1819]

  [3.1046]
  + let (a, b) = ("Pl", "ng");
• replacement in rust/raindrops/src/lib.rs at line 4
  [3.1047]→[2.51:190](∅→∅)
  − [(3, "i"), (5, "a"), (7, "o")].iter().for_each(|(d, e)| {

  − if n % d == 0 {

  − c.push_str(a);

  − c.push_str(e);

  − c.push_str(b)

  − }

  − });
  [3.1047]

  [2.190]
  + let c =

  + [(3, "i"), (5, "a"), (7, "o")]

  + .iter()

  + .fold(String::with_capacity(15), |mut d, (e, f)| {

  + if n % e == 0 {

  + d.push_str(a);

  + d.push_str(f);

  + d.push_str(b);

  + }

  + d

  + });