Added move_to_front_encoding implementation

DIRECTORY.md

@@ -46,6 +46,7 @@
     * [Xor](https://github.com/TheAlgorithms/Rust/blob/master/src/ciphers/xor.rs)
   * Compression
     * [Run Length Encoding](https://github.com/TheAlgorithms/Rust/blob/master/src/compression/run_length_encoding.rs)
+    * [Move-To-Front Encoding](https://github.com/TheAlgorithms/Rust/blob/master/src/compression/move_to_front.rs)
   * Conversions
     * [Binary To Decimal](https://github.com/TheAlgorithms/Rust/blob/master/src/conversions/binary_to_decimal.rs)
     * [Binary To Hexadecimal](https://github.com/TheAlgorithms/Rust/blob/master/src/conversions/binary_to_hexadecimal.rs)

src/compression/mod.rs

@@ -1,3 +1,5 @@
+mod move_to_front;
 mod run_length_encoding;
 
+pub use self::move_to_front::{move_to_front_decode, move_to_front_encode};
 pub use self::run_length_encoding::{run_length_decode, run_length_encode};

src/compression/move_to_front.rs

@@ -0,0 +1,60 @@
+// https://en.wikipedia.org/wiki/Move-to-front_transform
+
+fn blank_char_table() -> Vec<char> {
+    (0..=255).map(|ch| ch as u8 as char).collect()
+}
+
+pub fn move_to_front_encode(text: &str) -> Vec<u8> {
+    let mut char_table = blank_char_table();
+    let mut result = Vec::new();
+
+    for ch in text.chars() {
+        if let Some(position) = char_table.iter().position(|&x| x == ch) {
+            result.push(position as u8);
+            char_table.remove(position);
+            char_table.insert(0, ch);
+        }
+    }
+
+    result
+}
+
+pub fn move_to_front_decode(encoded: &[u8]) -> String {
+    let mut char_table = blank_char_table();
+    let mut result = String::new();
+
+    for &pos in encoded {
+        let ch = char_table[pos as usize];
+        result.push(ch);
+        char_table.remove(pos as usize);
+        char_table.insert(0, ch);
+    }
+
+    result
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    macro_rules! test_mtf {
+        ($($name:ident: ($text:expr, $encoded:expr),)*) => {
+            $(
+                #[test]
+                fn $name() {
+                    assert_eq!(move_to_front_encode($text), $encoded);
+                    assert_eq!(move_to_front_decode($encoded), $text);
+                }
+            )*
+        }
+    }
+
+    test_mtf! {
+        empty: ("", &[]),
+        single_char: ("@", &[64]),
+        repeated_chars: ("aaba", &[97, 0, 98, 1]),
+        mixed_chars: ("aZ!", &[97, 91, 35]),
+        word: ("banana", &[98, 98, 110, 1, 1, 1]),
+        special_chars: ("\0\n\t", &[0, 10, 10]),
+    }
+}