dsalgo 0.3.7

#[derive(Debug)]
pub struct NonDAGError {
    msg: &'static str,
}

impl NonDAGError {
    fn new() -> Self { Self { msg: "Given graph is not DAG." } }
}

impl std::fmt::Display for NonDAGError {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        write!(f, "{}", self.msg)
    }
}

impl std::error::Error for NonDAGError {
    fn description(&self) -> &str { &self.msg }
}

pub fn with_dfs(g: &Vec<Vec<usize>>) -> Result<Vec<usize>, NonDAGError> {
    fn dfs(
        g: &Vec<Vec<usize>>,
        state: &mut Vec<u8>,
        result: &mut Vec<usize>,
        u: usize,
    ) -> Result<(), NonDAGError> {
        if state[u] == 1 {
            return Err(NonDAGError::new());
        }
        if state[u] == 2 {
            return Ok(());
        }
        state[u] = 1;
        for &v in g[u].iter() {
            dfs(g, state, result, v)?;
        }
        state[u] = 2;
        result.push(u);
        Ok(())
    }
    let n = g.len();
    let mut state = vec![0u8; n];
    let mut result = Vec::with_capacity(n);
    for i in 0..n {
        if state[i] != 0 {
            continue;
        }
        if let Err(err) = dfs(g, &mut state, &mut result, i) {
            return Err(err);
        }
    }
    Ok(result.into_iter().rev().collect())
}

pub fn kahn(g: &Vec<Vec<usize>>) -> Result<Vec<usize>, NonDAGError> {
    let n = g.len();
    let mut in_deg = vec![0u32; n];
    for u in 0..n {
        for v in g[u].iter() {
            in_deg[*v] += 1;
        }
    }
    let mut que = std::collections::VecDeque::new();
    for (i, d) in in_deg.iter().enumerate() {
        if *d == 0 {
            que.push_back(i);
        }
    }
    let mut res = Vec::with_capacity(n);
    while let Some(u) = que.pop_front() {
        res.push(u);
        for &v in g[u].iter() {
            in_deg[v] -= 1;
            if in_deg[v] == 0 {
                que.push_back(v);
            }
        }
    }
    if in_deg.iter().all(|x| *x == 0) {
        Ok(res)
    } else {
        Err(NonDAGError::new())
    }
}