Lovecraft: try_all

lib.rs

fn try_all(grid: &Grid, 
        seen: &mut HashMap<Grid,Vec<Pos>>,
        todo: &mut VecDeque<Grid>
    ) -> Option<Vec<Pos>> {
    let path= match seen.get(grid){
        Some(p) => p.clone(),
        None => panic!("no path to grid!")
    };
    for a in 0..4 {
        for b in 0..4 {
            let g =swap(&grid,(a,b));
            let mut path = path.clone();
            path.push((a,b));
            match seen.get(&g){
                Some(v) => if v.len()>path.len() {
                    seen.insert(g,path.clone());
                },
                None => {
                    seen.insert(g,path.clone());
                    todo.push_back(g);
                },
            }

            if is_solved(g){
                return Some(path);
            }
        }
    }
    None

}