Data commit

Task/Run-length-encoding/Rust/run-length-encoding.rust

@@ -0,0 +1,55 @@
+fn encode(s: &str) -> String {
+    s.chars()
+        // wrap all values in Option::Some
+        .map(Some)
+        // add an Option::None onto the iterator to clean the pipeline at the end
+        .chain(std::iter::once(None))
+        .scan((0usize, '\0'), |(n, c), elem| match elem {
+            Some(elem) if *n == 0 || *c == elem => {
+                // the run continues or starts here
+                *n += 1;
+                *c = elem;
+                // this will not have an effect on the final string because it is empty
+                Some(String::new())
+            }
+            Some(elem) => {
+                // the run ends here
+                let run = format!("{}{}", n, c);
+                *n = 1;
+                *c = elem;
+                Some(run)
+            }
+            None => {
+                // the string ends here
+                Some(format!("{}{}", n, c))
+            }
+        })
+        // concatenate together all subresults
+        .collect()
+}
+
+fn decode(s: &str) -> String {
+    s.chars()
+        .fold((0usize, String::new()), |(n, text), c| {
+            if c.is_ascii_digit() {
+                // some simple number parsing
+                (
+                    n * 10 + c.to_digit(10).expect("invalid encoding") as usize,
+                    text,
+                )
+            } else {
+                // this must be the character that is repeated
+                (0, text + &format!("{}", c.to_string().repeat(n)))
+            }
+        })
+        .1
+}
+
+fn main() {
+    let text = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW";
+    let encoded = encode(text);
+    let decoded = decode(&encoded);
+
+    println!("original: {}\n encoded: {}\n decoded: {}", text, encoded, decoded);
+    assert_eq!(text, decoded);
+}