cubic.rs

use std::mem;

#[derive(Copy, Clone, Eq, PartialEq, Debug)]
struct Walk {
    axis: u32,
    positive: bool,
}

#[derive(Debug, Copy, Clone)]
struct Coord {
    coord: [u32; 3],
}

impl Coord {
    fn is_valid_walk(&self, walk: &Walk) -> bool {
        let coord = self.coord[walk.axis as usize];
        if walk.positive { coord <= 1 } else { coord >= 1 }
    }

    fn plus(&self, walk: &Walk) -> Coord {
        assert!(self.is_valid_walk(walk));
        let mut coord = self.clone();
        if walk.positive {
            coord.coord[walk.axis as usize] += 1;
        } else {
            coord.coord[walk.axis as usize] -= 1;
        }
        coord
    }
}

#[derive(Default, Copy, Clone, Debug)]
struct Visited {
    cells: [[[bool; 3]; 3]; 3],
    count: u32,
}

impl Visited {
    fn try_set_xyz(&mut self, coord: Coord) -> bool {
        let r = mem::replace(&mut self.cells[coord.coord[0] as usize][coord.coord[1] as usize][coord.coord[2] as usize], true);
        if !r {
            self.count += 1;
            assert!(self.count <= 27);
        }
        r
    }

    fn set_xyz(&mut self, coord: Coord) {
        assert!(!self.try_set_xyz(coord), "{:?} {:?}", coord, self);
    }

    fn get(&self, coord: Coord) -> bool {
        self.cells[coord.coord[0] as usize][coord.coord[1] as usize][coord.coord[2] as usize]
    }
}

fn continue_from(coord: Coord, mut visited: Visited, last_walk: Walk) {
    if visited.count == 27 {
        println!("yes");
        return;
    }
    if visited.try_set_xyz(coord) {
        //println!("breaking at {:?} {:?} {:?}", coord, visited, last_walk);
        //println!("breaking at {}", visited.count);
        return;
    }
    for axis in 0..=2 {
        for &positive in &[true, false] {
            let walk = Walk {
                axis,
                positive,
            };
            if walk == last_walk {
                continue;
            }
            if !coord.is_valid_walk(&walk) {
                continue;
            }
            let next_coord = coord.plus(&walk);
            continue_from(next_coord, visited, walk);
        }
    }
}

fn try_from(coord: Coord) {
    let mut visited = Visited::default();
    visited.set_xyz(coord);
    for axis in 0..=2 {
        for &positive in &[true, false] {
            let walk = Walk {
                axis,
                positive,
            };
            if !coord.is_valid_walk(&walk) {
                continue;
            }
            let next_coord = coord.plus(&walk);
            continue_from(next_coord, visited, walk);
        }
    }
}

fn main() {
    for x in 0..=2 {
        for y in 0..=2 {
            for z in 0..=2 {
                try_from(Coord { coord: [x, y, z] });
            }
        }
    }
    println!("$");
}