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

use crate::vector_unique::vector_unique;

pub struct CompressionResult<T> {
    pub keys: Vec<usize>,
    pub values: Vec<T>,
}

pub fn compress<T: Ord + Clone>(slice: &[T]) -> CompressionResult<T> {
    let values = vector_unique(slice.to_vec());
    let keys = slice
        .iter()
        .map(|x| values.binary_search(x).unwrap())
        .collect::<Vec<_>>();
    CompressionResult { keys, values }
}

pub struct ArrayCompression<T: Ord + Clone> {
    values: Vec<T>,
}

impl<T: Ord + Clone> ArrayCompression<T> {
    pub fn new(slice: &[T]) -> Self {
        Self {
            values: vector_unique(slice.to_vec()),
        }
    }

    pub fn encode(&self, value: &T) -> Option<usize> {
        if let Ok(key) = self.values.binary_search(value) {
            Some(key)
        } else {
            None
        }
    }

    pub fn decode(&self, key: usize) -> T { self.values[key].clone() }
}

#[cfg(test)]
mod tests {
    #[test]
    fn test() {
        let arr = [4, 3, 0, -1, 3, 10];
        let compression = super::ArrayCompression::new(&arr);
        assert_eq!(
            compression.encode(&-1).unwrap(),
            0
        );
        assert_eq!(
            compression.encode(&10).unwrap(),
            4
        );
        assert_eq!(compression.decode(0), -1);
        assert_eq!(compression.encode(&5), None);

        let result = super::compress(&arr);
        assert_eq!(
            result.keys,
            vec![3, 2, 1, 0, 2, 4]
        );
        assert_eq!(
            result.values,
            vec![-1, 0, 3, 4, 10]
        );
    }
}