librualg 0.29.1

Collection of basic algorithms for everyday development
Documentation 
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use std::collections::{BTreeMap, BinaryHeap};
use std::cmp::Ordering;
use std::ops::Add;

/// Huffman algorithm.
///```
/// use librualg::huffman::Huffman;
///
/// let (bytes, table) = Huffman::encode("abracadabra").unwrap();
/// let msg = Huffman::decode(&bytes, &table);
/// assert_eq!(msg, "abracadabra");
/// ```
pub struct Huffman {

}

#[derive(Clone, Eq, PartialEq)]
struct Edge {
    value: Option<u8>,
    children: Box<Option<[Edge; 2]>>,
}

#[derive(Clone, Eq, PartialEq)]
struct Pair {
    weight: i32,
    edge: Edge
}

impl Ord for Pair {
    fn cmp(&self, other: &Self) -> Ordering {
        other.weight.cmp(&self.weight).reverse()
    }
}

impl PartialOrd for Pair {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.weight.cmp(&other.weight).reverse())
    }
}

impl Huffman {
    pub fn encode(text: &str) -> Option<(Vec<u8>, BTreeMap<String, u8>)> {
        let mut dict = BTreeMap::new();
        let mut length = 0usize;
        for ch in text.as_bytes() {
            let entry = dict.entry(ch).or_insert(0i32);
            *entry += 1;
        }
        let mut values = dict.iter().map(|(key, value)| Pair{weight: *value, edge: Edge{value: Some(**key), children:Box::new(None)}}).collect::<BinaryHeap<Pair>>();
        if values.len() == 1 {
            let first = values.pop();
            let second = first.clone();
            let weight = first.as_ref().unwrap().weight;
            values.push(Pair{ weight, edge: Edge{value: None, children: Box::new(Some([first.unwrap().edge, second.unwrap().edge]))}});
        }
        while values.len() > 1 {
            let first = values.pop();
            let second = values.pop();
            let weight = first.as_ref().unwrap().weight + second.as_ref().unwrap().weight;
            values.push(Pair{ weight, edge: Edge{value: None, children: Box::new(Some([first.unwrap().edge, second.unwrap().edge]))}});
        }
        if !values.is_empty() {
            let mut encode_table = BTreeMap::new();
            let mut decode_table = BTreeMap::new();
            extract_character_codes(&values.pop().unwrap().edge, "".to_string(), &mut encode_table);
            for (key, value) in &encode_table {
                length += *dict.get(key).unwrap() as usize * value.len();
                decode_table.insert(value.clone(), *key);
            }

            let mut data: Vec<u8> = vec![0; length / 8 + match length % 8 {0 => 0,  _ => 1 } + 1];
            data[0] = (data.len() * 8 - length) as u8;
            let mut idx = data.len() * 8 - length;
            for ch in text.as_bytes() {
                for bit in encode_table.get(ch).unwrap().as_bytes() {
                    if *bit == b'1' {
                        let mask = 128 >> (idx % 8);
                        data[idx / 8] |= mask
                    }
                    idx += 1;
                }
            }
            return Some((data, decode_table));
        }
        None
    }
    pub fn decode(bytes: &[u8], decode_table: &BTreeMap<String, u8>) -> String {
        let mut idx = bytes[0] as usize;
        let mut res = String::new();
        let mut ch = String::new();
        while idx < bytes.len() * 8 {
            let mask = 128 >> (idx % 8);
            if bytes[idx / 8] & mask == mask {
                ch = ch.add("1");
            } else {
                ch = ch.add("0");
            }
            if let Some(value) = decode_table.get(&ch) {
                res.push(char::from(*value));
                ch.clear();
            }
            idx += 1;
        }
        res
    }
}

fn extract_character_codes(edge: &Edge, code: String, table: &mut BTreeMap<u8, String>) {
    if let Some(ch) = edge.value {
        table.insert(ch, code);
    } else if let Some(ref children) = *edge.children {
        extract_character_codes(&children[0], code.clone().add("0"), table);
        extract_character_codes(&children[1], code.add("1"), table);
    }
}


#[test]
fn test(){

    assert_eq!(Huffman::encode(""), None);

    let (bytes, decode_table) = Huffman::encode("abracadabra").unwrap();
    let msg = Huffman::decode(&bytes, &decode_table);
    assert_eq!(msg, "abracadabra");

    let (bytes, decode_table) = Huffman::encode("aaa").unwrap();
    let msg = Huffman::decode(&bytes, &decode_table);
    assert_eq!(msg, "aaa");

    let (bytes, decode_table) = Huffman::encode("a").unwrap();
    let msg = Huffman::decode(&bytes, &decode_table);
    assert_eq!(msg, "a");

    let (bytes, decode_table) = Huffman::encode(" a ").unwrap();
    let msg = Huffman::decode(&bytes, &decode_table);
    assert_eq!(msg, " a ");

    let (bytes, decode_table) = Huffman::encode(" a \n").unwrap();
    let msg = Huffman::decode(&bytes, &decode_table);
    assert_eq!(msg, " a \n");

    let (bytes, decode_table) = Huffman::encode("aaaaaaaa").unwrap();
    let msg = Huffman::decode(&bytes, &decode_table);
    assert_eq!(msg, "aaaaaaaa");
    assert_eq!(bytes.len(), 2);

}