创建 Atbash 密码的实现,这是在中东创建的古老加密系统.

Atbash 密码是一种简单的替换密码,它依赖于转置字母表中的所有字母,使得生成的字母表向后。

• 第一个字母替换为最后一个字母,
• 第二个字母替换为倒数第二个字母,
• 依此类推.

拉丁字母的 Atbash 密码如下:

明文:  abcdefghijklmnopqrstuvwxyz
加密:  zyxwvutsrqponmlkjihgfedcba

它是一个非常弱的加密方式，因为它只有一个加密可能性，且为一个简单的单字母替换密码。但是,这并不是现在’加密游戏-练习时间’的问题.

密文以固定长度的组写出，传统的组大小为 5 个字母，并且不包括标点符号。这是为了使单词边界，更难猜测。

• test，编码为gvhg
• gvhg，解码为test
• gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt解码为thequickbrownfoxjumpsoverthelazydog

维基百科http://en.wikipedia.org/wiki/Atbash

/// "Encipher" with the Atbash cipher.
pub fn encode(plain: &str) -> String {
   unimplemented!("Encoding of {:?} in Atbash cipher.", plain);
}

/// "Decipher" with the Atbash cipher.
pub fn decode(cipher: &str) -> String {
   unimplemented!("Decoding of {:?} in Atbash cipher.", cipher);
}

# #![allow(unused_variables)]
#fn main() {
#[test]
fn test_encode_yes() {
   assert_eq!("bvh", encode("yes"));
}

#[test]
//#[ignore]
fn test_encode_no() {
   assert_eq!("ml", encode("no"));
}

#[test]
//#[ignore]
fn test_encode_omg() {
   assert_eq!("lnt", encode("OMG"));
}

#[test]
//#[ignore]
fn test_encode_spaces() {
   assert_eq!("lnt", encode("O M G"));
}

#[test]
//#[ignore]
fn test_encode_mindblowingly() {
   assert_eq!("nrmwy oldrm tob", encode("mindblowingly"));
}

#[test]
//#[ignore]
fn test_encode_numbers() {
   assert_eq!("gvhgr mt123 gvhgr mt", encode("Testing,1 2 3, testing."));
}

#[test]
//#[ignore]
fn test_encode_deep_thought() {
   assert_eq!("gifgs rhurx grlm", encode("Truth is fiction."));
}

#[test]
//#[ignore]
fn test_encode_all_the_letters() {
   assert_eq!(
       "gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt",
       encode("The quick brown fox jumps over the lazy dog.")
   );
}

#[test]
//#[ignore]
fn test_encode_ignores_non_ascii() {
   assert_eq!("mlmzh xrrrt mlivw", encode("non ascii éignored"));
}

#[test]
//#[ignore]
fn test_decode_exercism() {
   assert_eq!("exercism", decode("vcvix rhn"));
}

#[test]
//#[ignore]
fn test_decode_a_sentence() {
   assert_eq!(
       "anobstacleisoftenasteppingstone",
       decode("zmlyh gzxov rhlug vmzhg vkkrm thglm v")
   );
}

#[test]
//#[ignore]
fn test_decode_numbers() {
   assert_eq!("testing123testing", decode("gvhgr mt123 gvhgr mt"));
}

#[test]
//#[ignore]
fn test_decode_all_the_letters() {
   assert_eq!(
       "thequickbrownfoxjumpsoverthelazydog",
       decode("gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt")
   );
}

#}

# #![allow(unused_variables)]
#fn main() {
fn ascii(ch: char) -> u8 {
   ch as u8
}

fn get_transpose(ch: char) -> char {
   if ch.is_digit(10) {
       ch
   } else {
       (ascii('z') - ascii(ch) + ascii('a')) as char
   }
}

pub fn encode(plaintext: &str) -> String {
   plaintext
       .to_lowercase()
       .chars()
       .filter(|&ch| ch.is_ascii())
       .filter(|&ch| ch.is_alphanumeric())
       .map(|ch| get_transpose(ch))
       .collect::<Vec<char>>()
       .chunks(5)
       .map(|slice| slice.iter().cloned().collect::<String>())
       .collect::<Vec<String>>()
       .join(" ")
}

pub fn decode(ciphertext: &str) -> String {
   ciphertext
       .split::<char>(' ')
       .collect::<String>()
       .chars()
       .map(|ch| get_transpose(ch))
       .collect::<String>()
}

#}