Main2.java

package afdw.jt;

import com.google.common.collect.ImmutableList;

import java.util.Arrays;
import java.util.List;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.stream.Collectors;
import java.util.stream.LongStream;

public class Main2 {
    private static final List<Shape> SHAPES = ImmutableList.<Shape>builder()
        .add(
            new Shape(
                "A",
                1,
                4,
                new boolean[][] {
                    {true},
                    {true},
                    {true},
                    {true}
                }
            )
        )
        .add(
            new Shape(
                "B",
                4,
                1,
                new boolean[][] {
                    {true, true, true, true}
                }
            )
        )
        .add(
            new Shape(
                "C",
                3,
                2,
                new boolean[][] {
                    {true, true, true},
                    {false, false, true}
                }
            )
        )
        .add(
            new Shape(
                "D",
                3,
                2,
                new boolean[][] {
                    {false, true, true},
                    {true, true, false}
                }
            )
        )
        .add(
            new Shape(
                "E",
                2,
                2,
                new boolean[][] {
                    {true, true},
                    {true, true}
                }
            )
        )
        .add(
            new Shape(
                "F",
                3,
                2,
                new boolean[][] {
                    {true, true, false},
                    {false, true, true}
                }
            )
        )
        .add(
            new Shape(
                "G",
                2,
                3,
                new boolean[][] {
                    {true, true},
                    {false, true},
                    {false, true}
                }
            )
        )
        .add(
            new Shape(
                "H",
                3,
                2,
                new boolean[][] {
                    {true, true, true},
                    {false, true, false}
                }
            )
        )
        .build();
    private static final int BOARD_SIZE = 6;

    @SuppressWarnings("SuspiciousNameCombination")
    public static void main(String[] args) {
        LongStream shapesPosesStream = LongStream.of(0);
        AtomicInteger maxFail = new AtomicInteger(0);
        int i = 0;
        for (Shape shape : SHAPES) {
            int finalI = i;
            shapesPosesStream = shapesPosesStream
                .flatMap(shapesPoses ->
                    LongStream.rangeClosed(0, BOARD_SIZE - shape.height)
                        .flatMap(y ->
                            LongStream.rangeClosed(0, BOARD_SIZE - shape.width)
                                .map(x -> x << 4 | y)
                        )
                        .map(pos -> shapesPoses << 8 | pos)
                )
                .filter(shapesPoses -> {
                    String[][] board = new String[BOARD_SIZE][BOARD_SIZE];
                    for (int j = 0; j <= finalI; j++) {
                        long pos = (shapesPoses >> ((finalI - j) * 8)) & 0b11111111;
                        if (!SHAPES.get(j).fillBoard(board, (int) ((pos >> 4) & 0b1111), (int) (pos & 0b1111))) {
                            if (j > maxFail.get()) {
                                maxFail.set(j);
                            }
                            return false;
                        }
                    }
                    return true;
                });
            i++;
        }
        shapesPosesStream = shapesPosesStream.parallel();
        List<String[][]> boards = shapesPosesStream
            .mapToObj(shapesPoses -> {
                String[][] board = new String[BOARD_SIZE][BOARD_SIZE];
                for (int j = 0; j < SHAPES.size(); j++) {
                    long pos = (shapesPoses >> ((SHAPES.size() - 1 - j) * 8)) & 0b11111111;
                    if (!SHAPES.get(j).fillBoard(board, (int) ((pos >> 4) & 0b1111), (int) (pos & 0b1111))) {
                        throw new IllegalStateException();
                    }
                }
                return board;
            })
            .collect(Collectors.toList());
        if (boards.isEmpty()) {
            System.out.println("Failed to place " + maxFail.get() + " shape");
        }
        System.out.println(
            boards.stream()
                .map(board ->
                    Arrays.stream(board)
                        .map(ss ->
                            Arrays.stream(ss)
                                .map(s -> s == null ? "." : s)
                                .collect(Collectors.joining(""))
                        )
                        .collect(Collectors.joining("\n"))
                )
                .collect(Collectors.joining("\n---\n"))
        );
    }

    private static final class Shape {
        @SuppressWarnings("WeakerAccess")
        public final String name;
        @SuppressWarnings("WeakerAccess")
        public final int width;
        @SuppressWarnings("WeakerAccess")
        public final int height;
        @SuppressWarnings("WeakerAccess")
        public final boolean[][] data;

        @SuppressWarnings("WeakerAccess")
        public Shape(String name, int width, int height, boolean[][] data) {
            this.name = name;
            this.width = width;
            this.height = height;
            this.data = data;
        }

        @SuppressWarnings("WeakerAccess")
        public boolean fillBoard(String[][] board, int startX, int startY) {
            for (int y = 0; y < height; y++) {
                for (int x = 0; x < width; x++) {
                    if (data[y][x]) {
                        if (board[startY + y][startX + x] != null) {
                            return false;
                        }
                        board[startY + y][startX + x] = name;
                    }
                }
            }
            return true;
        }
    }
}