实现编码和解码.

游程编码(RLE)是一种简单的数据压缩形式，其中运行的(连续数据元素)仅由一个数据值和计数代替。

例如,我们可以只用 13 字节，就可以 代表原始的 53 个字符.

"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB"  ->  "12WB12W3B24WB"

RLE 允许从压缩数据中，完美地重建原始数据,这使其成为无损数据压缩.

"AABCCCDEEEE"  ->  "2AB3CD4E"  ->  "AABCCCDEEEE"

为简单起见,您可以假设未编码的字符串，仅包含字母 A 到 Z(小写或大写)和空格。这样,要编码的数据将永远 不包含 任何数字,并且要解码的数据内的数字始终表示后续字符的计数。

维基百科https://en.wikipedia.org/wiki/Run-length_encoding

pub fn encode(source: &str) -> String {
   unimplemented!("Return the run-length encoding of {}.", source);
}

pub fn decode(source: &str) -> String {
   unimplemented!("Return the run-length decoding of {}.", source);
}

# #![allow(unused_variables)]
#fn main() {
// encoding tests

#[test]
fn test_encode_empty_string() {
   assert_eq!("", encode(""));
}

#[test]
//#[ignore]
fn test_encode_single_characters() {
   assert_eq!("XYZ", encode("XYZ"));
}

#[test]
//#[ignore]
fn test_encode_string_with_no_single_characters() {
   assert_eq!("2A3B4C", encode("AABBBCCCC"));
}

#[test]
//#[ignore]
fn test_encode_single_characters_mixed_with_repeated_characters() {
   assert_eq!(
       "12WB12W3B24WB",
       encode("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB")
   );
}

#[test]
//#[ignore]
fn test_encode_multiple_whitespace_mixed_in_string() {
   assert_eq!("2 hs2q q2w2 ", encode("  hsqq qww  "));
}

#[test]
//#[ignore]
fn test_encode_lowercase_characters() {
   assert_eq!("2a3b4c", encode("aabbbcccc"));
}

// decoding tests

#[test]
//#[ignore]
fn test_decode_empty_string() {
   assert_eq!("", decode(""));
}

#[test]
//#[ignore]
fn test_decode_single_characters_only() {
   assert_eq!("XYZ", decode("XYZ"));
}

#[test]
//#[ignore]
fn test_decode_string_with_no_single_characters() {
   assert_eq!("AABBBCCCC", decode("2A3B4C"));
}

#[test]
//#[ignore]
fn test_decode_single_characters_with_repeated_characters() {
   assert_eq!(
       "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB",
       decode("12WB12W3B24WB")
   );
}

#[test]
//#[ignore]
fn test_decode_multiple_whitespace_mixed_in_string() {
   assert_eq!("  hsqq qww  ", decode("2 hs2q q2w2 "));
}

#[test]
//#[ignore]
fn test_decode_lower_case_string() {
   assert_eq!("aabbbcccc", decode("2a3b4c"));
}

// consistency test

#[test]
//#[ignore]
fn test_consistency() {
   assert_eq!("zzz ZZ  zZ", decode(encode("zzz ZZ  zZ").as_str()));
}

#}

# #![allow(unused_variables)]
#fn main() {
use std::cmp;

pub fn encode(input: &str) -> String {
   input
       .chars()
       .fold(
           (String::new(), ' ', 0, 1),
           |(mut acc, last, last_n, pos), c| {
               // acc = where answer is accumulated
               // last = last character read
               // last_n = accum count for last
               if c == last {
                   if pos == input.len() {
                       // end of string
                       acc += (last_n + 1).to_string().as_str();
                       acc.push(c);
                   }
                   (acc, last, last_n + 1, pos + 1)
               } else {
                   if last_n > 1 {
                       acc += last_n.to_string().as_str();
                   }
                   if last_n > 0 {
                       // ignore initial last (single whitespace)
                       acc.push(last);
                   }
                   if pos == input.len() {
                       // end of string
                       acc.push(c);
                   }
                   (acc, c, 1, pos + 1)
               }
           },
       )
       .0
}

pub fn decode(input: &str) -> String {
   input
       .chars()
       .fold((String::new(), 0), |(mut acc, last_n), c| {
           if let Some(d) = c.to_digit(10) {
               (acc, 10 * last_n + d)
           } else {
               acc += c.to_string().repeat(cmp::max(last_n, 1) as usize).as_str();
               (acc, 0)
           }
       })
       .0
}

#}