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#![no_std] extern crate alloc; use alloc::{ collections::{binary_heap::BinaryHeap, BTreeMap}, rc::Rc, string::String, vec::Vec, }; use core::cmp::Ordering; pub fn frequency(n: &str) -> BTreeMap<char, i32> { let mut output: BTreeMap<char, i32> = BTreeMap::new(); n.chars().for_each(|c| { let new = if let Some(o) = output.get(&c) { o + 1i32 } else { 1i32 }; output.insert(c, new); }); output } pub struct Codec(pub BTreeMap<char, Vec<u8>>); impl Codec { pub fn new(s: &str) -> Self { fn map_to_heap(map: BTreeMap<char, i32>) -> BinaryHeap<Rc<Tree>> { let mut heap = BinaryHeap::new(); map.into_iter().for_each(|(l, c)| { let t = Tree::new(l, c); heap.push(t); }); heap } fn heap_to_tree(mut heap: BinaryHeap<Rc<Tree>>) -> Rc<Tree> { while heap.len() > 1 { let (t1, t2) = (heap.pop().unwrap(), heap.pop().unwrap()); heap.push(Tree::merge(t1, t2)); } heap.pop().unwrap() } fn tree_to_codes( root: &Option<Rc<Tree>>, prefix: Vec<u8>, mut map: BTreeMap<char, Vec<u8>>, ) -> BTreeMap<char, Vec<u8>> { if let Some(ref tree) = *root { match tree.value { Some(t) => { map.insert(t, prefix); } None => { let (mut prefix_l, mut prefix_r) = (prefix.clone(), prefix); prefix_l.push(1u8); let map = tree_to_codes(&tree.left, prefix_l, map); prefix_r.push(0u8); return tree_to_codes(&tree.right, prefix_r, map); } } } map } let f_map = frequency(s); let heap = map_to_heap(f_map); let tree = heap_to_tree(heap); Self(tree_to_codes(&Some(tree), Vec::new(), BTreeMap::new())) } pub fn encode(&self, data: &str) -> Result<Vec<u8>, CharDNEinDict> { let mut nbits = 0; data.chars() .try_for_each(|c| -> Result<(), CharDNEinDict> { if let Some(code) = self.0.get(&c) { nbits += code.len(); Ok(()) } else { Err(CharDNEinDict) } })?; let mut ret = Vec::<u8>::with_capacity(nbits); data.chars().for_each(|c| { let v = self .0 .get(&c) .expect("checked existence in first for loop above; qed"); v.iter().for_each(|bit| ret.push(*bit)); }); Ok(ret) } pub fn decode(&self, data: Vec<u8>) -> String { fn reverse(h: &BTreeMap<char, Vec<u8>>) -> BTreeMap<Vec<u8>, char> { let mut ret = BTreeMap::new(); h.iter().for_each(|(k, v)| { ret.insert(v.clone(), *k); }); ret } let code = reverse(&self.0); let mut temp = Vec::<u8>::new(); let mut ret = String::new(); data.into_iter().for_each(|b| { temp.push(b); if let Some(c) = code.get(&temp) { ret.push(*c); temp.clear(); } }); ret } } #[derive(Eq, Debug, Clone)] struct Tree { count: i32, value: Option<char>, left: Option<Rc<Tree>>, right: Option<Rc<Tree>>, } impl Ord for Tree { fn cmp(&self, other: &Tree) -> Ordering { (self.count).cmp(&(other.count)) } } impl PartialOrd for Tree { fn partial_cmp(&self, other: &Tree) -> Option<Ordering> { Some(self.cmp(other)) } } impl PartialEq for Tree { fn eq(&self, other: &Tree) -> bool { self.count == other.count } } impl Tree { fn new(value: char, count: i32) -> Rc<Tree> { let t = Tree { count, value: Some(value), left: None, right: None, }; Rc::new(t) } fn merge(tree_smaller: Rc<Tree>, tree_larger: Rc<Tree>) -> Rc<Tree> { let t = Tree { count: tree_smaller.count + tree_larger.count, value: None, left: Some(tree_smaller), right: Some(tree_larger), }; Rc::new(t) } } #[derive(Debug)] pub struct CharDNEinDict; #[cfg(test)] mod tests { use super::*; #[test] fn frequency_works() { let a = "aaaabbbcccddddabababa"; let res_fn = frequency(a); let mut res: BTreeMap<char, i32> = BTreeMap::new(); res.insert('a', 8); res.insert('b', 6); res.insert('c', 3); res.insert('d', 4); assert_eq!(res_fn, res); } #[test] fn decoding_works() { let a = "aaaabbbcccddddaaabababr"; let a1 = "abracadabra"; let codec = Codec::new(a); let encoded = codec.encode(a1).unwrap(); let decoded = codec.decode(encoded); assert_eq!(a1, decoded); let a2 = "abcdr"; let encoded = codec.encode(a2).unwrap(); let decoded = codec.decode(encoded); assert_eq!(a2, decoded); let a3 = "x"; assert!(codec.encode(a3).is_err()); } }