A pentomino is a polyomino that consists of 5 squares. There are 12 pentomino shapes,
if you don't count rotations and reflections. Most pentominoes can form their own mirror image through
rotation, but some of them have to be flipped over.

        I                                                                        
        I     L       N                                                 Y        
 FF     I     L      NN     PP     TTT              V       W     X    YY      ZZ
FF      I     L      N      PP      T     U U       V      WW    XXX    Y      Z 
 F      I     LL     N      P       T     UUU     VVV     WW      X     Y     ZZ


A Pentomino tiling is an example of an exact cover problem and can take on many forms.
A traditional tiling presents an 8 by 8 grid, where 4 cells are left uncovered. The other cells are covered
by the 12 pentomino shapes, without overlaps, with every shape only used once.

The 4 uncovered cells should be chosen at random. Note that not all configurations are solvable.



Task
Create an 8 by 8 tiling and print the result.



Example
F I I I I I L N
F F F L L L L N
W F - X Z Z N N
W W X X X Z N V
T W W X - Z Z V
T T T P P V V V
T Y - P P U U U
Y Y Y Y P U - U


Related tasks
 Free polyominoes enumeration


package pentominotiling;
 
import java.util.*;
 
public class PentominoTiling {
 
    static final char[] symbols = "FILNPTUVWXYZ-".toCharArray();
    static final Random rand = new Random();
 
    static final int nRows = 8;
    static final int nCols = 8;
    static final int blank = 12;
 
    static int[][] grid = new int[nRows][nCols];
    static boolean[] placed = new boolean[symbols.length - 1];
 
    public static void main(String[] args) {
        shuffleShapes();
 
        for (int r = 0; r < nRows; r++)
            Arrays.fill(grid[r], -1);
 
        for (int i = 0; i < 4; i++) {
            int randRow, randCol;
            do {
                randRow = rand.nextInt(nRows);
                randCol = rand.nextInt(nCols);
            } while (grid[randRow][randCol] == blank);
            grid[randRow][randCol] = blank;
        }
 
        if (solve(0, 0)) {
            printResult();
        } else {
            System.out.println("no solution");
        }
    }
 
    static void shuffleShapes() {
        int n = shapes.length;
        while (n > 1) {
            int r = rand.nextInt(n--);
 
            int[][] tmp = shapes[r];
            shapes[r] = shapes[n];
            shapes[n] = tmp;
 
            char tmpSymbol = symbols[r];
            symbols[r] = symbols[n];
            symbols[n] = tmpSymbol;
        }
    }
 
    static void printResult() {
        for (int[] r : grid) {
            for (int i : r)
                System.out.printf("%c ", symbols[i]);
            System.out.println();
        }
    }
 
    static boolean tryPlaceOrientation(int[] o, int r, int c, int shapeIndex) {
 
        for (int i = 0; i < o.length; i += 2) {
            int x = c + o[i + 1];
            int y = r + o[i];
            if (x < 0 || x >= nCols || y < 0 || y >= nRows || grid[y][x] != -1)
                return false;
        }
 
        grid[r][c] = shapeIndex;
        for (int i = 0; i < o.length; i += 2)
            grid[r + o[i]][c + o[i + 1]] = shapeIndex;
 
        return true;
    }
 
    static void removeOrientation(int[] o, int r, int c) {
        grid[r][c] = -1;
        for (int i = 0; i < o.length; i += 2)
            grid[r + o[i]][c + o[i + 1]] = -1;
    }
 
    static boolean solve(int pos, int numPlaced) {
        if (numPlaced == shapes.length)
            return true;
 
        int row = pos / nCols;
        int col = pos % nCols;
 
        if (grid[row][col] != -1)
            return solve(pos + 1, numPlaced);
 
        for (int i = 0; i < shapes.length; i++) {
            if (!placed[i]) {
                for (int[] orientation : shapes[i]) {
 
                    if (!tryPlaceOrientation(orientation, row, col, i))
                        continue;
 
                    placed[i] = true;
 
                    if (solve(pos + 1, numPlaced + 1))
                        return true;
 
                    removeOrientation(orientation, row, col);
                    placed[i] = false;
                }
            }
        }
        return false;
    }
 
    static final int[][] F = {{1, -1, 1, 0, 1, 1, 2, 1}, {0, 1, 1, -1, 1, 0, 2, 0},
    {1, 0, 1, 1, 1, 2, 2, 1}, {1, 0, 1, 1, 2, -1, 2, 0}, {1, -2, 1, -1, 1, 0, 2, -1},
    {0, 1, 1, 1, 1, 2, 2, 1}, {1, -1, 1, 0, 1, 1, 2, -1}, {1, -1, 1, 0, 2, 0, 2, 1}};
 
    static final int[][] I = {{0, 1, 0, 2, 0, 3, 0, 4}, {1, 0, 2, 0, 3, 0, 4, 0}};
 
    static final int[][] L = {{1, 0, 1, 1, 1, 2, 1, 3}, {1, 0, 2, 0, 3, -1, 3, 0},
    {0, 1, 0, 2, 0, 3, 1, 3}, {0, 1, 1, 0, 2, 0, 3, 0}, {0, 1, 1, 1, 2, 1, 3, 1},
    {0, 1, 0, 2, 0, 3, 1, 0}, {1, 0, 2, 0, 3, 0, 3, 1}, {1, -3, 1, -2, 1, -1, 1, 0}};
 
    static final int[][] N = {{0, 1, 1, -2, 1, -1, 1, 0}, {1, 0, 1, 1, 2, 1, 3, 1},
    {0, 1, 0, 2, 1, -1, 1, 0}, {1, 0, 2, 0, 2, 1, 3, 1}, {0, 1, 1, 1, 1, 2, 1, 3},
    {1, 0, 2, -1, 2, 0, 3, -1}, {0, 1, 0, 2, 1, 2, 1, 3}, {1, -1, 1, 0, 2, -1, 3, -1}};
 
    static final int[][] P = {{0, 1, 1, 0, 1, 1, 2, 1}, {0, 1, 0, 2, 1, 0, 1, 1},
    {1, 0, 1, 1, 2, 0, 2, 1}, {0, 1, 1, -1, 1, 0, 1, 1}, {0, 1, 1, 0, 1, 1, 1, 2},
    {1, -1, 1, 0, 2, -1, 2, 0}, {0, 1, 0, 2, 1, 1, 1, 2}, {0, 1, 1, 0, 1, 1, 2, 0}};
 
    static final int[][] T = {{0, 1, 0, 2, 1, 1, 2, 1}, {1, -2, 1, -1, 1, 0, 2, 0},
    {1, 0, 2, -1, 2, 0, 2, 1}, {1, 0, 1, 1, 1, 2, 2, 0}};
 
    static final int[][] U = {{0, 1, 0, 2, 1, 0, 1, 2}, {0, 1, 1, 1, 2, 0, 2, 1},
    {0, 2, 1, 0, 1, 1, 1, 2}, {0, 1, 1, 0, 2, 0, 2, 1}};
 
    static final int[][] V = {{1, 0, 2, 0, 2, 1, 2, 2}, {0, 1, 0, 2, 1, 0, 2, 0},
    {1, 0, 2, -2, 2, -1, 2, 0}, {0, 1, 0, 2, 1, 2, 2, 2}};
 
    static final int[][] W = {{1, 0, 1, 1, 2, 1, 2, 2}, {1, -1, 1, 0, 2, -2, 2, -1},
    {0, 1, 1, 1, 1, 2, 2, 2}, {0, 1, 1, -1, 1, 0, 2, -1}};
 
    static final int[][] X = {{1, -1, 1, 0, 1, 1, 2, 0}};
 
    static final int[][] Y = {{1, -2, 1, -1, 1, 0, 1, 1}, {1, -1, 1, 0, 2, 0, 3, 0},
    {0, 1, 0, 2, 0, 3, 1, 1}, {1, 0, 2, 0, 2, 1, 3, 0}, {0, 1, 0, 2, 0, 3, 1, 2},
    {1, 0, 1, 1, 2, 0, 3, 0}, {1, -1, 1, 0, 1, 1, 1, 2}, {1, 0, 2, -1, 2, 0, 3, 0}};
 
    static final int[][] Z = {{0, 1, 1, 0, 2, -1, 2, 0}, {1, 0, 1, 1, 1, 2, 2, 2},
    {0, 1, 1, 1, 2, 1, 2, 2}, {1, -2, 1, -1, 1, 0, 2, -2}};
 
    static final int[][][] shapes = {F, I, L, N, P, T, U, V, W, X, Y, Z};
}