searchlib 0.1.2

Satisficing and optimal search algorithms
Documentation 
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//! [Depth First Search](https://en.wikipedia.org/wiki/Depth-first_search)

use crate::{trace, FxIndexMap};
use indexmap::map::Entry::Vacant;
use std::hash::Hash;

pub struct DFS<STATE, SUCCESSORS, SUCCESS, ITER>
where
    STATE: Eq + Hash + Clone,
    SUCCESSORS: FnMut(&STATE) -> ITER,
    SUCCESS: FnMut(&STATE) -> bool,
    ITER: IntoIterator<Item = STATE>,
{
    stack: Vec<usize>,
    states: FxIndexMap<STATE, usize>,
    successors: SUCCESSORS,
    success: SUCCESS,
}

impl<STATE, SUCCESSORS, SUCCESS, ITER> DFS<STATE, SUCCESSORS, SUCCESS, ITER>
where
    STATE: Eq + Hash + Clone,
    SUCCESSORS: FnMut(&STATE) -> ITER,
    SUCCESS: FnMut(&STATE) -> bool,
    ITER: IntoIterator<Item = STATE>,
{
    pub fn new(init: &STATE, successors: SUCCESSORS, success: SUCCESS) -> Self {
        let mut states = FxIndexMap::default();
        states.insert(init.clone(), 0);
        Self {
            stack: vec![0],
            states,
            successors,
            success,
        }
    }
}

impl<STATE, SUCCESSORS, SUCCESS, ITER> Iterator for DFS<STATE, SUCCESSORS, SUCCESS, ITER>
where
    STATE: Eq + Hash + Clone,
    SUCCESSORS: FnMut(&STATE) -> ITER,
    SUCCESS: FnMut(&STATE) -> bool,
    ITER: IntoIterator<Item = STATE>,
{
    type Item = Option<Vec<STATE>>;

    fn next(&mut self) -> Option<Self::Item> {
        let index = self.stack.pop()?;
        let (node, _) = self.states.get_index(index).unwrap();
        if (self.success)(&node) {
            return Some(Some(trace(&self.states, index)));
        }
        for successor in (self.successors)(node) {
            if let Vacant(e) = self.states.entry(successor) {
                let index = {
                    let i = e.index();
                    e.insert(index);
                    i
                };
                self.stack.push(index);
            }
        }
        Some(None)
    }
}

pub fn solve<STATE, SUCCESSORS, SUCCESS, ITER>(
    init: &STATE,
    successors: SUCCESSORS,
    success: SUCCESS,
) -> Option<Vec<STATE>>
where
    STATE: Eq + Hash + Clone,
    SUCCESSORS: FnMut(&STATE) -> ITER,
    SUCCESS: FnMut(&STATE) -> bool,
    ITER: IntoIterator<Item = STATE>,
{
    DFS::new(init, successors, success)
        .into_iter()
        .find(|i| i.is_some())?
}

pub fn paths<STATE, SUCCESSORS, SUCCESS, ITER>(
    init: &STATE,
    successors: SUCCESSORS,
    success: SUCCESS,
) -> impl Iterator<Item = Vec<STATE>>
where
    STATE: Eq + Hash + Clone,
    SUCCESSORS: FnMut(&STATE) -> ITER,
    SUCCESS: FnMut(&STATE) -> bool,
    ITER: IntoIterator<Item = STATE>,
{
    DFS::new(init, successors, success)
        .into_iter()
        .filter_map(|i| i)
}