competitive_programming_rs/graph/
topological_sort.rs

1pub fn topological_sort(graph: &[Vec<usize>]) -> Vec<usize> {
2    let n = graph.len();
3    let mut in_deg = vec![0; n];
4    for v in 0..n {
5        for &to in graph[v].iter() {
6            in_deg[to] += 1;
7        }
8    }
9
10    let mut q = std::collections::VecDeque::new();
11    for i in 0..n {
12        if in_deg[i] == 0 {
13            q.push_back(i);
14        }
15    }
16
17    let mut result = vec![];
18    while let Some(v) = q.pop_front() {
19        for &next in graph[v].iter() {
20            in_deg[next] -= 1;
21            if in_deg[next] == 0 {
22                q.push_back(next);
23            }
24        }
25
26        result.push(v);
27    }
28    result
29}
30
31#[cfg(test)]
32mod tests {
33    use super::*;
34
35    #[test]
36    fn test_topological_sort() {
37        let graph = vec![vec![1], vec![2], vec![], vec![1, 4], vec![5], vec![2]];
38        let result = topological_sort(&graph);
39        assert_eq!(vec![0, 3, 1, 4, 5, 2], result);
40    }
41}