September Morn Update

Task/Move-to-front-algorithm/00META.yaml

@@ -0,0 +1 @@
+--- {}

Task/Move-to-front-algorithm/Aime/move-to-front-algorithm.aime

@@ -1,13 +1,13 @@
 text
 decode(list l)
 {
-    integer c, e, i;
-    text al, s;
+    integer c, e;
+    data al, s;
 
     al = "abcdefghijklmnopqrstuvwxyz";
-    for (i, e in l) {
-        s = insert(s, -1, c = al[e]);
-        al = insert(delete(al, e), 0, c);
+    for (, e in l) {
+        s.append(c = al[e]);
+        al.delete(e).insert(0, c);
     }
 
     s;
@@ -17,14 +17,13 @@ list
 encode(text s)
 {
     integer c, e;
-    text al;
+    data al;
     list l;
 
     al = "abcdefghijklmnopqrstuvwxyz";
-    while (c = initial(s)) {
-        s = delete(s, 0);
-        l.append(e = place(al, c));
-        al = insert(delete(al, e), 0, c);
+    for (, c in b_draft(s)) {
+        l.append(e = al.place(c));
+        al.delete(e).insert(0, c);
     }
 
     l;
@@ -33,10 +32,7 @@ encode(text s)
 integer
 main(void)
 {
-    integer i;
-    text s;
-
-    for (i, s in list("broood", "bananaaa", "hiphophiphop")) {
+    for (, text s in list("broood", "bananaaa", "hiphophiphop")) {
         list l;
 
         l = encode(s);

Task/Move-to-front-algorithm/Factor/move-to-front-algorithm.factor

@@ -0,0 +1,18 @@
+USING: formatting kernel locals make sequences ;
+
+: to-front ( elt seq -- seq' ) over [ remove ] dip prefix ;
+
+: encode ( symbols msg -- indices )
+    [ [ swap 2dup index , to-front ] each ] { } make nip ;
+
+: decode ( symbols indices -- msg )
+    [ [ swap [ nth ] keep over , to-front ] each ] "" make nip ;
+
+:: round-trip ( msg symbols -- )
+    symbols msg encode :> encoded
+    symbols encoded decode :> decoded
+    msg decoded assert=
+    msg encoded decoded "%s -> %u -> %s\n" printf ;
+
+"broood" "bananaaa" "hiphophiphop"
+[ "abcdefghijklmnopqrstuvwxyz" round-trip ] tri@

Task/Move-to-front-algorithm/Rust/move-to-front-algorithm.rust

@@ -0,0 +1,44 @@
+fn main() {
+    let examples = vec!["broood", "bananaaa", "hiphophiphop"];
+    for example in examples {
+        let encoded = encode(example);
+        let decoded = decode(&encoded);
+        println!(
+            "{} encodes to {:?} decodes to {}",
+            example, encoded, decoded
+        );
+    }
+}
+
+fn get_symbols() -> Vec<u8> {
+    (b'a'..b'z').collect()
+}
+
+fn encode(input: &str) -> Vec<usize> {
+    input
+        .as_bytes()
+        .iter()
+        .fold((Vec::new(), get_symbols()), |(mut o, mut s), x| {
+            let i = s.iter().position(|c| c == x).unwrap();
+            let c = s.remove(i);
+            s.insert(0, c);
+            o.push(i);
+            (o, s)
+        })
+        .0
+}
+
+fn decode(input: &[usize]) -> String {
+    input
+        .iter()
+        .fold((Vec::new(), get_symbols()), |(mut o, mut s), x| {
+            o.push(s[*x]);
+            let c = s.remove(*x);
+            s.insert(0, c);
+            (o, s)
+        })
+        .0
+        .into_iter()
+        .map(|c| c as char)
+        .collect()
+}