1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148

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);

}