algos 0.6.8

A collection of algorithms in Rust
Documentation 
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

use rand::Rng;
use std::cell::RefCell;
use std::rc::Rc;

type Link<T> = Option<Rc<RefCell<SkipNode<T>>>>;

#[derive(Debug)]
pub struct SkipNode<T> {
    pub value: Option<T>,
    pub forward: Vec<Link<T>>,
}

#[derive(Debug)]
pub struct SkipList<T> {
    head: Rc<RefCell<SkipNode<T>>>,
    pub max_level: usize,
    pub p: f64,
    pub current_level: usize,
}

impl<T: Ord> SkipList<T> {
    /// Creates a new empty skip list with a specified maximum level and probability for level promotion.
    pub fn new(max_level: usize, p: f64) -> Self {
        let head = Rc::new(RefCell::new(SkipNode {
            value: None,
            forward: vec![None; max_level],
        }));
        SkipList {
            head,
            max_level,
            p,
            current_level: 1,
        }
    }

    /// Randomly determines a level for a new node based on probability p.
    fn random_level(&self) -> usize {
        let mut lvl = 1;
        let mut rng = rand::thread_rng();
        while rng.gen::<f64>() < self.p && lvl < self.max_level {
            lvl += 1;
        }
        lvl
    }

    /// Inserts a value into the skip list.
    pub fn insert(&mut self, value: T) {
        let mut update: Vec<Rc<RefCell<SkipNode<T>>>> = vec![self.head.clone(); self.max_level];
        let mut current = self.head.clone();
        // Traverse levels from top to bottom.
        for i in (0..self.current_level).rev() {
            loop {
                let forward = current.borrow().forward[i].clone();
                match forward {
                    Some(next) => {
                        if next.borrow().value.as_ref().unwrap() < &value {
                            current = next;
                        } else {
                            break;
                        }
                    }
                    None => break,
                }
            }
            update[i] = current.clone();
        }
        // Determine node level.
        let lvl = self.random_level();
        if lvl > self.current_level {
            update
                .iter_mut()
                .skip(self.current_level)
                .take(lvl - self.current_level)
                .for_each(|x| *x = self.head.clone());
            self.current_level = lvl;
        }
        let new_node = Rc::new(RefCell::new(SkipNode {
            value: Some(value),
            forward: vec![None; lvl],
        }));
        // Splice the new node into the list.
        for (i, update_node) in update.iter().take(lvl).enumerate() {
            let next = update_node.borrow().forward[i].clone();
            new_node.borrow_mut().forward[i] = next;
            update_node.borrow_mut().forward[i] = Some(new_node.clone());
        }
    }

    /// Searches for a value in the skip list. Returns true if the value is present.
    pub fn search(&self, value: &T) -> bool {
        let mut current = self.head.clone();
        for i in (0..self.current_level).rev() {
            loop {
                let forward = current.borrow().forward[i].clone();
                match forward {
                    Some(next) => {
                        if next.borrow().value.as_ref().unwrap() < value {
                            current = next;
                        } else {
                            break;
                        }
                    }
                    None => break,
                }
            }
        }
        let forward = current.borrow().forward[0].clone();
        if let Some(next) = forward {
            next.borrow().value.as_ref().unwrap() == value
        } else {
            false
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_skip_list_insert_search() {
        let mut skip_list = SkipList::new(16, 0.5);
        skip_list.insert(10);
        skip_list.insert(20);
        skip_list.insert(15);
        skip_list.insert(5);

        assert!(skip_list.search(&10));
        assert!(skip_list.search(&15));
        assert!(skip_list.search(&20));
        assert!(skip_list.search(&5));
        assert!(!skip_list.search(&25));
    }
}