Iterative.rs

pub fn solution<'a>(
    board_stack: &mut VecDeque<(Board, Vec<ChessPiece>)>,
    solutions: &'a mut HashSet<Board>,
    tested_configurations: &mut HashSet<Board>,
) -> &'a HashSet<Board> {
    while !board_stack.is_empty() {
        let (board, pieces) = board_stack.pop_back().unwrap();
        for row in 1..=board.m {
            for col in 1..=board.n {
                let new_piece = Piece {
                    row,
                    col,
                    piece: pieces[0],
                };
                if board.is_safe(new_piece) {
                    let new_board = board.place(new_piece);
                    if pieces.len() != 1 {
                        if tested_configurations.insert(new_board.clone()) {
                            let next_board = new_board.clone();
                            let tail = Vec::from_iter(pieces[1..pieces.len()].iter().cloned());
                            board_stack.push_front((next_board, tail));
                        }
                    } else {
                        solutions.insert(new_board);
                    }
                }
            }
        }
    }
    solutions
}