cot 0.6.0

The Rust web framework for lazy developers.
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
135
136

use thiserror::Error;

#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, Error)]
#[error("cycle detected in the graph")]
pub struct CycleDetected;

#[doc(hidden)] // not part of public API, used in the Cot CLI
pub fn apply_permutation<T>(items: &mut [T], order: &mut [usize]) {
    for i in 0..order.len() {
        let mut current = i;
        let mut next = order[current];

        while next != i {
            // process the cycle
            items.swap(current, next);
            order[current] = current;

            current = next;
            next = order[current];
        }

        order[current] = current;
    }
}

#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub(crate) struct Graph {
    vertex_edges: Vec<Vec<usize>>,
}

impl Graph {
    #[must_use]
    pub(crate) fn new(vertex_num: usize) -> Self {
        Self {
            vertex_edges: vec![Vec::new(); vertex_num],
        }
    }

    pub(crate) fn add_edge(&mut self, from: usize, to: usize) {
        self.vertex_edges[from].push(to);
    }

    #[must_use]
    pub(crate) fn vertex_num(&self) -> usize {
        self.vertex_edges.len()
    }

    pub(crate) fn toposort(&mut self) -> Result<Vec<usize>, CycleDetected> {
        let mut visited = vec![VisitedStatus::NotVisited; self.vertex_num()];
        let mut sorted_indices_stack = Vec::with_capacity(self.vertex_num());

        for index in (0..self.vertex_num()).rev() {
            self.toposort_visit(index, &mut visited, &mut sorted_indices_stack)?;
        }

        assert_eq!(sorted_indices_stack.len(), self.vertex_num());

        sorted_indices_stack.reverse();
        Ok(sorted_indices_stack)
    }

    #[expect(clippy::indexing_slicing)]
    fn toposort_visit(
        &self,
        index: usize,
        visited: &mut Vec<VisitedStatus>,
        sorted_indices_stack: &mut Vec<usize>,
    ) -> Result<(), CycleDetected> {
        match visited[index] {
            VisitedStatus::Visited => return Ok(()),
            VisitedStatus::Visiting => {
                return Err(CycleDetected);
            }
            VisitedStatus::NotVisited => {}
        }

        visited[index] = VisitedStatus::Visiting;

        for &neighbor in &self.vertex_edges[index] {
            self.toposort_visit(neighbor, visited, sorted_indices_stack)?;
        }

        visited[index] = VisitedStatus::Visited;
        sorted_indices_stack.push(index);

        Ok(())
    }
}

#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
enum VisitedStatus {
    NotVisited,
    Visiting,
    Visited,
}

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

    #[test]
    fn graph_toposort_stable() {
        let mut graph = Graph::new(8);
        let sorted_indices = graph.toposort().unwrap();
        assert_eq!(sorted_indices, vec![0, 1, 2, 3, 4, 5, 6, 7]);
    }

    #[test]
    fn graph_toposort() {
        let mut graph = Graph::new(8);
        graph.add_edge(5, 3);
        graph.add_edge(1, 3);
        graph.add_edge(1, 2);
        graph.add_edge(4, 2);
        graph.add_edge(4, 6);
        graph.add_edge(3, 0);
        graph.add_edge(3, 7);
        graph.add_edge(3, 6);
        graph.add_edge(2, 7);

        let sorted_indices = graph.toposort().unwrap();

        assert_eq!(sorted_indices, vec![1, 4, 2, 5, 3, 0, 6, 7]);
    }

    #[test]
    fn graph_toposort_with_cycle() {
        let mut graph = Graph::new(4);
        graph.add_edge(0, 1);
        graph.add_edge(1, 2);
        graph.add_edge(2, 3);
        graph.add_edge(3, 0);

        assert!(matches!(graph.toposort(), Err(CycleDetected)));
    }
}