The problem is to make a program the flips a 2D (2 by 2) array either horizontally(H) or vertically(V), depending on the input the user puts. For example, if the user puts "HHHVVHVHV", it means to flip 5 times horizontally, and 4 times vertically. The code I attached below works, but I am not sure if there is a built-in method in C# to flip arrays or an easier way to do it.
using System;
using System.Linq;
namespace _2019JuniorQ4
{
class Program
{
static void Main(string[] args)
{
//Varables
int[,] grid = new int[2, 2] { { 1, 2 }, { 3, 4 } };
int[,] flippedGrid = new int[2, 2];
string input = "";
int h = 0;
int v = 0;
int flipHorizontal = 0;
int flipVertical = 0;
//Input
input = Console.ReadLine();
//Count number of times
for (int i=0; i<input.Length; i++)
{
if (input[i] == Convert.ToChar("H"))
{
h++;
}
else if(input[i] == Convert.ToChar("V"))
{
v++;
}
}
//Process
flipHorizontal = h % 2;
flipVertical = v % 2;
//Vertical flip
if (flipVertical == 1)
{
for (int y = 0; y < 2; y++)
{
for (int x = 1; x >= 0; x--)
{
flippedGrid[y, Math.Abs(x - 1)] = grid[y,x];
}
}
grid = flippedGrid.Clone() as int[,];
}
//Horizontal Flip
if (flipHorizontal == 1)
{
for (int x = 0; x < 2; x++)
{
for (int y = 1; y >= 0; y--)
{
flippedGrid[Math.Abs(y - 1), x] = grid[y,x];
}
}
grid = flippedGrid.Clone() as int[,];
}
//Output
for (int x=0; x<2; x++)
{
for (int y=0; y<2; y++)
{
Console.Write(grid[x,y]+" ");
}
Console.WriteLine();
}
}
}
}
I want to fill my array with struct in a way that it will look like this
I have this code so far :
`for (int i = 1; i <= n; i++)
{
for (int j = 0; j <=(n - i); j++)
//i should fill m[,] here
for (int j = 1; j <= i; j++)
//i should fill m[,] here
for (int k = 1; k < i; k++)
//i should fill m[,] here
}
for (int i = n - 1; i >= 1; i--)
{
for (int j = 0; j < (n - i); j++)
//i should fill m[,] here
for (int j = 1; j <= i; j++)
//i should fill m[,] here
for (int k = 1; k < i; k++)
//i should fill m[,] here
}`
but I 'm a little bit confused with the index .
how can I adopt this code?
As it's unclear wether the array always has the size 5 I'll assume it has the size n with n being odd and n > 0 (The size is the x and the y size, as I assume that your matrix is quadratic). Then there are several ways to reach the goal your trying to reach, I'll try to present you one I thought of.
First of all we have to think about the array - as it's the easiest way, I'll assume it consists of boolean values (even though you said "I want to fill my array with struct", but as I'm not quite sure what you wanted to say with that and wether you really meant a struct, I'll let this up to you, as this shouldn't be the most difficult part):
var matrix = new bool[n,n];
Then we have to evalueate which fields have to be filled. Therefore we must realize a few things:
The filled fields are always central in their line
The first and last line always have one filled item
The following line always has two more/less filled items, so that the offset is one more than in the previous line
The center line has most items and is the turning point in the amount of filled items
As a first step in developing the algorithm, I'd write a function to fill lines of the array with specific amounts of fields:
private static void FillLine(int line, int count, bool[,] matrix)
{
//Firstly we have to evaluate the offset:
var offset = (matrix.GetLength(0) - count) / 2;
//Then we have to fill the line
for (var x = offset; x < offset + count; x++)
matrix[x, line] = true;
}
Now we simply have to fill the lines for the whole array:
public static void FillDiamond(bool[,] matrix)
{
var count = 1;
for (var line = 0; line < matrix.GetLength(1) / 2; line++)
{
FillLine(line, count, matrix);
count += 2;
}
FillLine(matrix.GetLength(1) / 2, count, matrix);
count = 1;
for (var line = matrix.GetLength(1) - 1; line > matrix.GetLength(1) / 2; line--)
{
FillLine(line, count, matrix);
count += 2;
}
}
Now in a console application you could use this like that:
using System;
namespace SO_c
{
internal static class Program
{
private static void Main()
{
while (true)
{
var n = int.Parse(Console.ReadLine());
if (n < 1 || n % 2 == 0)
continue;
var matrix = new bool[n, n];
FillDiamond(matrix);
for (var y = 0; y < matrix.GetLength(1); y++)
{
for (var x = 0; x < matrix.GetLength(0); x++)
Console.Write(matrix[x, y] ? "█" : " ");
Console.WriteLine();
}
}
}
private static void FillLine(int line, int count, bool[,] matrix)
{
//Firstly we have to evaluate the offset:
var offset = (matrix.GetLength(0) - count) / 2;
//Then we have to fill the line
for (var x = offset; x < offset + count; x++)
matrix[x, line] = true;
}
public static void FillDiamond(bool[,] matrix)
{
var count = 1;
for (var line = 0; line < matrix.GetLength(1) / 2; line++)
{
FillLine(line, count, matrix);
count += 2;
}
FillLine(matrix.GetLength(1) / 2, count, matrix);
count = 1;
for (var line = matrix.GetLength(1) - 1; line > matrix.GetLength(1) / 2; line--)
{
FillLine(line, count, matrix);
count += 2;
}
}
}
}
This can result in output like that:
That's it! Now you should get your diamond for every matrix that fits the rules :)
One way to do it is to calculate the center of the grid and fill in each row, from the center column. In each successive row, we increment the number of blocks we fill in on each side of the center column until we get to the center row, and then we decrement the number of blocks we fill in until we get to the end.
To determine how many blocks to put on each side of the center column for any given row, we can use the row index for the calculation.
Working our way from the top down to the center, the row index represents the number of blocks to add. So, for row index 0, we add 0 blocks on either side of the center column, row index 1 we add 1 block on each side, until we get to the center.
After we get to the center, we want to decrement the number of blocks each time, which can be done by subtracting the row index from the total number of rows.
The code says it better, I think:
private static void Main()
{
while (true)
{
// Get grid size from user and keep it between 1 and the window width
var gridSize = GetIntFromUser("Enter the size of the grid: ");
gridSize = Math.Min(Console.WindowWidth - 1, Math.Max(1, gridSize));
var grid = new bool[gridSize, gridSize];
var center = (gridSize - 1) / 2;
// Populate our grid with a diamond pattern
for (int rowIndex = 0; rowIndex < grid.GetLength(0); rowIndex++)
{
// Determine number of blocks to fill based on current row
var fillAmount = (rowIndex <= center)
? rowIndex : grid.GetUpperBound(0) - rowIndex;
for (int colIndex = 0; colIndex <= fillAmount; colIndex++)
{
grid[rowIndex, center - colIndex] = true;
grid[rowIndex, center + colIndex] = true;
}
}
// Display the final grid to the console
for (int row = 0; row < grid.GetLength(0); row++)
{
for (int col = 0; col < grid.GetLength(1); col++)
{
Console.Write(grid[row, col] ? "█" : " ");
}
Console.WriteLine();
}
}
}
Oh, and this is the helper function I used to get an integer from the user. It's pretty helpful to keep around because you don't have to do any validation in your main code:
private static int GetIntFromUser(string prompt)
{
int value;
// Write the prompt text and get input from user
Console.Write(prompt);
string input = Console.ReadLine();
// If input can't be converted to a double, keep trying
while (!int.TryParse(input, out value))
{
Console.Write($"'{input}' is not a valid number. Please try again: ");
input = Console.ReadLine();
}
// Input was successfully converted!
return value;
}
OUTPUT
I am having a little problem here, I want to draw a vertical pyramid like this:
O
OO
OOO
OOOO
OOOOO
OOOO
OOO
OO
O
But I can't seem to figure out how to do it. All I get is:
O
OO
OOO
OOOO
OOOOO
OOOOOO
OOOOOOO
OOOOOOOO
OOOOOOOOO
Here is my code:
int width = 5;
for (int y = 1; y < width * 2; y++)
{
for (int x = 0; x < y; x++)
{
Console.Write("O");
}
Console.WriteLine();
}
There are ways to do this with two loops, but here is a way to do it with one, and without an if condition:
for (int y = 1; y < width * 2; y++)
{
int numOs = width - Math.Abs(width - y);
for (int x = 0; x < numOs; x++)
{
Console.Write("O");
}
Console.WriteLine();
}
use this code maybe useful
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication59
{
class Program
{
static void Main(string[] args)
{
int numberoflayer = 6, Space, Number;
Console.WriteLine("Print paramid");
for (int i = 1; i <= numberoflayer; i++) // Total number of layer for pramid
{
for (Space = 1; Space <= (numberoflayer - i); Space++) // Loop For Space
Console.Write(" ");
for (Number = 1; Number <= i; Number++) //increase the value
Console.Write(Number);
for (Number = (i - 1); Number >= 1; Number--) //decrease the value
Console.Write(Number);
Console.WriteLine();
}
}
}
}
Here is a minimalist method with only one loop and one ternary expression (?) instead of if:
int width = 5;
for (int y = 1; y < width * 2; y++)
Console.WriteLine(String.Empty.PadLeft(y < width ? y : width * 2 - y, 'O'));
Or a version without check:
for (int y = 1; y < width * 2; y++)
Console.WriteLine(String.Empty.PadLeft(Math.Abs(width * (y / width) - (y % width)), 'O'));
I need help with my map editor, I'm stuck on saving it. When I save, after I put some grass on map, it gets grass everywhere in map file.
Here's variables:
mapMaximumX: maximum of the map in X (it is set as 500)
mapMaximumY: maximum of the map in Y (it is also set as 500)
mapTiles[index]: this is a list with class, each class has ID (0 = empty, 1 = grass, 2 = water), X and Y
if (Keyboard.GetState().IsKeyDown(Keys.F1))
{
for(int y = 0; y < mapMaximumY; y++)
{
for (int x = 0; x < mapMaximumX; x++)
{
if (MapTiles[i3].X == x && MapTiles[i3].Y == y)
{
}
else
{
MapTiles.Add(new Class1(0, x * 32, y * 32));
}
if (i3 < MapTiles.Count)
{
i3++;
}
}
}
TextWriter file = new StreamWriter("map1.MAP");
for (int y = 0; y < mapMaximumY; y++)
{
for (int x = 0; x < mapMaximumX; x++)
{
file.Write(MapTiles[i2].ID + ", ");
}
file.Write(file.NewLine);
}
i2 = 0;
System.Windows.Forms.MessageBox.Show("Saved!");
file.Close();
}
Full code is here, if u need it:
http://pastebin.com/qrWbuPtb
Thanx.
file.Write(MapTiles[i2].ID + ", ");
i2 never changes within your loop, so whatever i2 is will always be what's used to write your output.
You need to be using X and Y from your loops in determining which cell to write out.
Please see my own answer, I think I did it!
Hi,
An example question for a programming contest was to write a program that finds out how much polyominos are possible with a given number of stones.
So for two stones (n = 2) there is only one polyominos:
XX
You might think this is a second solution:
X
X
But it isn't. The polyominos are not unique if you can rotate them.
So, for 4 stones (n = 4), there are 7 solutions:
X
X XX X X X X
X X XX X XX XX XX
X X X XX X X XX
The application has to be able to find the solution for 1 <= n <=10
PS: Using the list of polyominos on Wikipedia isn't allowed ;)
EDIT: Of course the question is: How to do this in Java, C/C++, C#
I started this project in Java. But then I had to admit I didn't know how to build polyominos using an efficient algorithm.
This is what I had so far:
import java.util.ArrayList;
import java.util.List;
public class Main
{
private int countPolyminos(int n)
{
hashes.clear();
count = 0;
boolean[][] matrix = new boolean[n][n];
createPolyominos(matrix, n);
return count;
}
private List<Integer> hashes = new ArrayList<Integer>();
private int count;
private void createPolyominos(boolean[][] matrix, int n)
{
if (n == 0)
{
boolean[][] cropped = cropMatrix(matrix);
int hash = hashMatrixOrientationIndependent(matrix);
if (!hashes.contains(hash))
{
count++;
hashes.add(hash);
}
return;
}
// Here is the real trouble!!
// Then here something like; createPolyominos(matrix, n-1);
// But, we need to keep in mind that the polyominos can have ramifications
}
public boolean[][] copy(boolean[][] matrix)
{
boolean[][] b = new boolean[matrix.length][matrix[0].length];
for (int i = 0; i < matrix.length; ++i)
{
System.arraycopy(matrix[i], 0, b, 0, matrix[i].length);
}
return b;
}
public boolean[][] cropMatrix(boolean[][] matrix)
{
int l = 0, t = 0, r = 0, b = 0;
// Left
left: for (int x = 0; x < matrix.length; ++x)
{
for (int y = 0; y < matrix[x].length; ++y)
{
if (matrix[x][y])
{
break left;
}
}
l++;
}
// Right
right: for (int x = matrix.length - 1; x >= 0; --x)
{
for (int y = 0; y < matrix[x].length; ++y)
{
if (matrix[x][y])
{
break right;
}
}
r++;
}
// Top
top: for (int y = 0; y < matrix[0].length; ++y)
{
for (int x = 0; x < matrix.length; ++x)
{
if (matrix[x][y])
{
break top;
}
}
t++;
}
// Bottom
bottom: for (int y = matrix[0].length; y >= 0; --y)
{
for (int x = 0; x < matrix.length; ++x)
{
if (matrix[x][y])
{
break bottom;
}
}
b++;
}
// Perform the real crop
boolean[][] cropped = new boolean[matrix.length - l - r][matrix[0].length - t - b];
for (int x = l; x < matrix.length - r; ++x)
{
System.arraycopy(matrix[x - l], t, cropped, 0, matrix[x].length - t - b);
}
return cropped;
}
public int hashMatrix(boolean[][] matrix)
{
int hash = 0;
for (int x = 0; x < matrix.length; ++x)
{
for (int y = 0; y < matrix[x].length; ++y)
{
hash += matrix[x][y] ? (((x + 7) << 4) * ((y + 3) << 6) * 31) : ((((x+5) << 9) * (((y + x) + 18) << 7) * 53));
}
}
return hash;
}
public int hashMatrixOrientationIndependent(boolean[][] matrix)
{
int hash = 0;
hash += hashMatrix(matrix);
for (int i = 0; i < 3; ++i)
{
matrix = rotateMatrixLeft(matrix);
hash += hashMatrix(matrix);
}
return hash;
}
public boolean[][] rotateMatrixRight(boolean[][] matrix)
{
/* W and H are already swapped */
int w = matrix.length;
int h = matrix[0].length;
boolean[][] ret = new boolean[h][w];
for (int i = 0; i < h; ++i)
{
for (int j = 0; j < w; ++j)
{
ret[i][j] = matrix[w - j - 1][i];
}
}
return ret;
}
public boolean[][] rotateMatrixLeft(boolean[][] matrix)
{
/* W and H are already swapped */
int w = matrix.length;
int h = matrix[0].length;
boolean[][] ret = new boolean[h][w];
for (int i = 0; i < h; ++i)
{
for (int j = 0; j < w; ++j)
{
ret[i][j] = matrix[j][h - i - 1];
}
}
return ret;
}
}
There are only 4,461 polynominoes of size 10, so we can just enumerate them all.
Start with a single stone. To expand it by one stone, try add the new stone in at all empty cells that neighbour an existing stone. Do this recursively until reaching the desired size.
To avoid duplicates, keep a hash table of all polynominoes of each size we've already enumerated. When we put together a new polynomino, we check that its not already in the hash table. We also need to check its 3 rotations (and possibly its mirror image). While duplicate checking at the final size is the only strictly necessary check, checking at each step prunes recursive branches that will yield a new polynomino.
Here's some pseudo-code:
polynomino = array of n hashtables
function find_polynominoes(n, base):
if base.size == n:
return
for stone in base:
for dx, dy in [(-1, 0), (1, 0), (0, -1), (0, 1)]:
new_stone.x = stone.x + dx
new_stone.y = stone.y + dy
if new_stone not in base:
new_polynomino = base + new_stone
is_new = true
for rotation in [0, 90, 180, 270]:
if new_polynomino.rotate(rotation) in polynomino[new_polynomino.size]:
is_new = false
break
if is_new:
polynomino[new_polynomino.size].add(new_polynomino)
Just solved this as well in java. Since all here appear to have performance issues. I give you mine as well.
Board reprsentation:
2 arrays of integers. 1 for the rows and 1 for the columns.
Rotation: column[i]=row[size-(i+1)], row[i] = reverse(column[i]) where reverse is the bits reversed according to the size (for size = 4 and first 2 bits are taken: rev(1100) = 0011)
Shifting block: row[i-1] = row[i], col[i]<<=1
Check if bit is set: (row[r] & (1<<c)) > 0
Board uniqueness: The board is unique when the array row is unique.
Board hash: Hashcode of the array row
..
So this makes all operations fast. Many of them would have been O(size²) in the 2D array representation instead of now O(size).
Algorithm:
Start with the block of size 1
For each size start from the blocks with 1 stone less.
If it's possible to add the stone. Check if it was already added to the set.
If it's not yet added. Add it to the solution of this size.
add the block to the set and all its rotations. (3 rotations, 4 in total)
Important, after each rotation shift the block as left/top as possible.
+Special cases: do the same logic for the next 2 cases
shift block one to the right and add stone in first column
shift block one to the bottom and add stone in first row
Performance:
N=5 , time: 3ms
N=10, time: 58ms
N=11, time: 166ms
N=12, time: 538ms
N=13, time: 2893ms
N=14, time:17266ms
N=15, NA (out of heapspace)
Code:
https://github.com/Samjayyy/logicpuzzles/tree/master/polyominos
The most naive solution is to start with a single X, and for each iteration, build the list of unique possible next-states. From that list, build the list of unique states by adding another X. Continue this until the iteration you desire.
I'm not sure if this runs in reasonable time for N=10, however. It might, depending on your requirements.
I think I did it!
EDIT: I'm using the SHA-256 algorithm to hash them, now it works correct.
Here are the results:
numberOfStones -> numberOfPolyominos
1 -> 1
2 -> 1
3 -> 2
4 -> 7
5 -> 18
6 -> 60
7 -> 196
8 -> 704
9 -> 2500
10 -> terminated
Here is the code (Java):
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
/* VPW Template */
public class Main
{
/**
* #param args
*/
public static void main(String[] args) throws IOException
{
new Main().start();
}
public void start() throws IOException
{
/* Read the stuff */
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String[] input = new String[Integer.parseInt(br.readLine())];
for (int i = 0; i < input.length; ++i)
{
input[i] = br.readLine();
}
/* Process each line */
for (int i = 0; i < input.length; ++i)
{
processLine(input[i]);
}
}
public void processLine(String line)
{
int n = Integer.parseInt(line);
System.out.println(countPolyminos(n));
}
private int countPolyminos(int n)
{
hashes.clear();
count = 0;
boolean[][] matrix = new boolean[n][n];
matrix[n / 2][n / 2] = true;
createPolyominos(matrix, n - 1);
return count;
}
private List<BigInteger> hashes = new ArrayList<BigInteger>();
private int count;
private void createPolyominos(boolean[][] matrix, int n)
{
if (n == 0)
{
boolean[][] cropped = cropMatrix(matrix);
BigInteger hash = hashMatrixOrientationIndependent(cropped);
if (!hashes.contains(hash))
{
// System.out.println(count + " Found!");
// printMatrix(cropped);
// System.out.println();
count++;
hashes.add(hash);
}
return;
}
for (int x = 0; x < matrix.length; ++x)
{
for (int y = 0; y < matrix[x].length; ++y)
{
if (matrix[x][y])
{
if (x > 0 && !matrix[x - 1][y])
{
boolean[][] clone = copy(matrix);
clone[x - 1][y] = true;
createPolyominos(clone, n - 1);
}
if (x < matrix.length - 1 && !matrix[x + 1][y])
{
boolean[][] clone = copy(matrix);
clone[x + 1][y] = true;
createPolyominos(clone, n - 1);
}
if (y > 0 && !matrix[x][y - 1])
{
boolean[][] clone = copy(matrix);
clone[x][y - 1] = true;
createPolyominos(clone, n - 1);
}
if (y < matrix[x].length - 1 && !matrix[x][y + 1])
{
boolean[][] clone = copy(matrix);
clone[x][y + 1] = true;
createPolyominos(clone, n - 1);
}
}
}
}
}
public boolean[][] copy(boolean[][] matrix)
{
boolean[][] b = new boolean[matrix.length][matrix[0].length];
for (int i = 0; i < matrix.length; ++i)
{
System.arraycopy(matrix[i], 0, b[i], 0, matrix[i].length);
}
return b;
}
public void printMatrix(boolean[][] matrix)
{
for (int y = 0; y < matrix.length; ++y)
{
for (int x = 0; x < matrix[y].length; ++x)
{
System.out.print((matrix[y][x] ? 'X' : ' '));
}
System.out.println();
}
}
public boolean[][] cropMatrix(boolean[][] matrix)
{
int l = 0, t = 0, r = 0, b = 0;
// Left
left: for (int x = 0; x < matrix.length; ++x)
{
for (int y = 0; y < matrix[x].length; ++y)
{
if (matrix[x][y])
{
break left;
}
}
l++;
}
// Right
right: for (int x = matrix.length - 1; x >= 0; --x)
{
for (int y = 0; y < matrix[x].length; ++y)
{
if (matrix[x][y])
{
break right;
}
}
r++;
}
// Top
top: for (int y = 0; y < matrix[0].length; ++y)
{
for (int x = 0; x < matrix.length; ++x)
{
if (matrix[x][y])
{
break top;
}
}
t++;
}
// Bottom
bottom: for (int y = matrix[0].length - 1; y >= 0; --y)
{
for (int x = 0; x < matrix.length; ++x)
{
if (matrix[x][y])
{
break bottom;
}
}
b++;
}
// Perform the real crop
boolean[][] cropped = new boolean[matrix.length - l - r][matrix[0].length - t - b];
for (int x = l; x < matrix.length - r; ++x)
{
System.arraycopy(matrix[x], t, cropped[x - l], 0, matrix[x].length - t - b);
}
return cropped;
}
public BigInteger hashMatrix(boolean[][] matrix)
{
try
{
MessageDigest md = MessageDigest.getInstance("SHA-256");
md.update((byte) matrix.length);
md.update((byte) matrix[0].length);
for (int x = 0; x < matrix.length; ++x)
{
for (int y = 0; y < matrix[x].length; ++y)
{
if (matrix[x][y])
{
md.update((byte) x);
} else
{
md.update((byte) y);
}
}
}
return new BigInteger(1, md.digest());
} catch (NoSuchAlgorithmException e)
{
System.exit(1);
return null;
}
}
public BigInteger hashMatrixOrientationIndependent(boolean[][] matrix)
{
BigInteger hash = hashMatrix(matrix);
for (int i = 0; i < 3; ++i)
{
matrix = rotateMatrixLeft(matrix);
hash = hash.add(hashMatrix(matrix));
}
return hash;
}
public boolean[][] rotateMatrixRight(boolean[][] matrix)
{
/* W and H are already swapped */
int w = matrix.length;
int h = matrix[0].length;
boolean[][] ret = new boolean[h][w];
for (int i = 0; i < h; ++i)
{
for (int j = 0; j < w; ++j)
{
ret[i][j] = matrix[w - j - 1][i];
}
}
return ret;
}
public boolean[][] rotateMatrixLeft(boolean[][] matrix)
{
/* W and H are already swapped */
int w = matrix.length;
int h = matrix[0].length;
boolean[][] ret = new boolean[h][w];
for (int i = 0; i < h; ++i)
{
for (int j = 0; j < w; ++j)
{
ret[i][j] = matrix[j][h - i - 1];
}
}
return ret;
}
Here's my solution in Java to the same problem. I can confirm Martijn's numbers (see below). I've also added in the rough time it takes to compute the results (mid-2012 Macbook Retina Core i7). I suppose substantial performance improvements could be achieved via parallelization.
numberOfStones -> numberOfPolyominos
1 -> 1
2 -> 1
3 -> 2
4 -> 7
5 -> 18
6 -> 60
7 -> 196
8 -> 704 (3 seconds)
9 -> 2500 (46 seconds)
10 -> 9189 (~14 minutes)
.
/*
* This class is a solution to the Tetris unique shapes problem.
* That is, the game of Tetris has 7 unique shapes. These 7 shapes
* are all the possible unique combinations of any 4 adjoining blocks
* (i.e. ignoring rotations).
*
* How many unique shapes are possible with, say, 7 or n blocks?
*
* The solution uses recursive back-tracking to construct all the possible
* shapes. It uses a HashMap to store unique shapes and to ignore rotations.
* It also uses a temporary HashMap so that the program does not needlessly
* waste time checking the same path multiple times.
*
* Even so, this is an exponential run-time solution, with n=10 taking a few
* minutes to complete.
*/
package com.glugabytes.gbjutils;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
public class TetrisBlocks {
private HashMap uShapes;
private HashMap tempShapes;
/* Get a map of unique shapes for n squares. The keys are string-representations
* of each shape, and values are corresponding boolean[][] arrays.
* #param squares - number of blocks to use for shapes, e.g. n=4 has 7 unique shapes
*/
public Map getUniqueShapes(int squares) {
uShapes = new HashMap();
tempShapes = new HashMap();
boolean[][] data = new boolean[squares*2+1][squares*2+1];
data[squares][squares] = true;
make(squares, data, 1); //start the process with a single square in the center of a boolean[][] matrix
return uShapes;
}
/* Recursivelly keep adding blocks to the data array until number of blocks(squares) = required size (e.g. n=4)
* Make sure to eliminate rotations. Also make sure not to enter infinite backtracking loops, and also not
* needlessly recompute the same path multiple times.
*/
private void make(int squares, boolean[][] data, int size) {
if(size == squares) { //used the required number of squares
//get a trimmed version of the array
boolean[][] trimmed = trimArray(data);
if(!isRotation(trimmed)) { //if a unique piece, add it to unique map
uShapes.put(arrayToString(trimmed), trimmed);
}
} else {
//go through the grid 1 element at a time and add a block next to an existing block
//do this for all possible combinations
for(int iX = 0; iX < data.length; iX++) {
for(int iY = 0; iY < data.length; iY++) {
if(data[iX][iY] == true) { //only add a block next to an existing block
if(data[iX+1][iY] != true) { //if no existing block to the right, add one and recuse
data[iX+1][iY] = true;
if(!isTempRotation(data)) { //only recurse if we haven't already been on this path before
make(squares, data, size+1);
tempShapes.put(arrayToString(data), data); //store this path so we don't repeat it later
}
data[iX+1][iY] = false;
}
if(data[iX-1][iY] != true) { //repeat by adding a block on the left
data[iX-1][iY] = true;
if(!isTempRotation(data)) {
make(squares, data, size+1);
tempShapes.put(arrayToString(data), data);
}
data[iX-1][iY] = false;
}
if(data[iX][iY+1] != true) { //repeat by adding a block down
data[iX][iY+1] = true;
if(!isTempRotation(data)) {
make(squares, data, size+1);
tempShapes.put(arrayToString(data), data);
}
data[iX][iY+1] = false;
}
if(data[iX][iY-1] != true) { //repeat by adding a block up
data[iX][iY-1] = true;
if(!isTempRotation(data)) {
make(squares, data, size+1);
tempShapes.put(arrayToString(data), data);
}
data[iX][iY-1] = false;
}
}
}
}
}
}
/**
* This function basically removes all rows and columns that have no 'true' flags,
* leaving only the portion of the array that contains useful data.
*
* #param data
* #return
*/
private boolean[][] trimArray(boolean[][] data) {
int maxX = 0;
int maxY = 0;
int firstX = data.length;
int firstY = data.length;
for(int iX = 0; iX < data.length; iX++) {
for (int iY = 0; iY < data.length; iY++) {
if(data[iX][iY]) {
if(iY < firstY) firstY = iY;
if(iY > maxY) maxY = iY;
}
}
}
for(int iY = 0; iY < data.length; iY++) {
for (int iX = 0; iX < data.length; iX++) {
if(data[iX][iY]) {
if(iX < firstX) firstX = iX;
if(iX > maxX) maxX = iX;
}
}
}
boolean[][] trimmed = new boolean[maxX-firstX+1][maxY-firstY+1];
for(int iX = firstX; iX <= maxX; iX++) {
for(int iY = firstY; iY <= maxY; iY++) {
trimmed[iX-firstX][iY-firstY] = data[iX][iY];
}
}
return trimmed;
}
/**
* Return a string representation of the 2D array.
*
* #param data
* #return
*/
private String arrayToString(boolean[][] data) {
StringBuilder sb = new StringBuilder();
for(int iX = 0; iX < data.length; iX++) {
for(int iY = 0; iY < data[0].length; iY++) {
sb.append(data[iX][iY] ? '#' : ' ');
}
sb.append('\n');
}
return sb.toString();
}
/**
* Rotate an array clockwise by 90 degrees.
* #param data
* #return
*/
public boolean[][] rotate90(boolean[][] data) {
boolean[][] rotated = new boolean[data[0].length][data.length];
for(int iX = 0; iX < data.length; iX++) {
for(int iY = 0; iY < data[0].length; iY++) {
rotated[iY][iX] = data[data.length - iX - 1][iY];
}
}
return rotated;
}
/**
* Checks to see if two 2d boolean arrays are the same
* #param a
* #param b
* #return
*/
public boolean equal(boolean[][] a, boolean[][] b) {
if(a.length != b.length || a[0].length != b[0].length) {
return false;
} else {
for(int iX = 0; iX < a.length; iX++) {
for(int iY = 0; iY < a[0].length; iY++) {
if(a[iX][iY] != b[iX][iY]) {
return false;
}
}
}
}
return true;
}
public boolean isRotation(boolean[][] data) {
//check to see if it's a rotation of a shape that we already have
data = rotate90(data); //+90*
String str = arrayToString(data);
if(!uShapes.containsKey(str)) {
data = rotate90(data); //180*
str = arrayToString(data);
if(!uShapes.containsKey(str)) {
data = rotate90(data); //270*
str = arrayToString(data);
if(!uShapes.containsKey(str)) {
return false;
}
}
}
return true;
}
public boolean isTempRotation(boolean[][] data) {
//check to see if it's a rotation of a shape that we already have
data = rotate90(data); //+90*
String str = arrayToString(data);
if(!tempShapes.containsKey(str)) {
data = rotate90(data); //180*
str = arrayToString(data);
if(!tempShapes.containsKey(str)) {
data = rotate90(data); //270*
str = arrayToString(data);
if(!tempShapes.containsKey(str)) {
return false;
}
}
}
return true;
}
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
TetrisBlocks tetris = new TetrisBlocks();
long start = System.currentTimeMillis();
Map shapes = tetris.getUniqueShapes(8);
long end = System.currentTimeMillis();
Iterator it = shapes.keySet().iterator();
while(it.hasNext()) {
String shape = (String)it.next();
System.out.println(shape);
}
System.out.println("Unique Shapes: " + shapes.size());
System.out.println("Time: " + (end-start));
}
}
Here's some python that computes the answer. Seems to agree with Wikipedia. It isn't terribly fast because it uses lots of array searches instead of hash tables, but it still takes only a minute or so to complete.
#!/usr/bin/python
# compute the canonical representation of polyomino p.
# (minimum x and y coordinate is zero, sorted)
def canonical(p):
mx = min(map(lambda v: v[0], p))
my = min(map(lambda v: v[1], p))
return sorted(map(lambda v: (v[0]-mx, v[1]-my), p))
# rotate p 90 degrees
def rotate(p):
return canonical(map(lambda v: (v[1], -v[0]), p))
# add one tile to p
def expand(p):
result = []
for (x,y) in p:
for (dx,dy) in ((-1,0),(1,0),(0,-1),(0,1)):
if p.count((x+dx,y+dy)) == 0:
result.append(canonical(p + [(x+dx,y+dy)]))
return result
polyominos = [[(0,0)]]
for i in xrange(1,10):
new_polyominos = []
for p in polyominos:
for q in expand(p):
dup = 0
for r in xrange(4):
if new_polyominos.count(q) != 0:
dup = 1
break
q = rotate(q)
if not dup: new_polyominos.append(q)
polyominos = new_polyominos
print i+1, len(polyominos)
Here is my full Python solution inspired by #marcog's answer. It prints the number of polyominos of sizes 2..10 in about 2s on my laptop.
The algorithm is straightforward:
Size 1: start with one square
Size n + 1: take all pieces of size n and try adding a single square to all possible adjacent positions. This way you find all possible new pieces of size n + 1. Skip duplicates.
The main speedup came from hashing pieces to quickly check if we've already seen a piece.
import itertools
from collections import defaultdict
n = 10
print("Number of Tetris pieces up to size", n)
# Times:
# n is number of blocks
# - Python O(exp(n)^2): 10 blocks 2.5m
# - Python O(exp(n)): 10 blocks 2.5s, 11 blocks 10.9s, 12 block 33s, 13 blocks 141s (800MB memory)
smallest_piece = [(0, 0)] # We represent a piece as a list of block positions
pieces_of_size = {
1: [smallest_piece],
}
# Returns a list of all possible pieces made by adding one block to given piece
def possible_expansions(piece):
# No flatMap in Python 2/3:
# https://stackoverflow.com/questions/21418764/flatmap-or-bind-in-python-3
positions = set(itertools.chain.from_iterable(
[(x - 1, y), (x + 1, y), (x, y - 1), (x, y + 1)] for (x, y) in piece
))
# Time complexity O(n^2) can be improved
# For each valid position, append to piece
expansions = []
for p in positions:
if not p in piece:
expansions.append(piece + [p])
return expansions
def rotate_90_cw(piece):
return [(y, -x) for (x, y) in piece]
def canonical(piece):
min_x = min(x for (x, y) in piece)
min_y = min(y for (x, y) in piece)
res = sorted((x - min_x, y - min_y) for (x, y) in piece)
return res
def hash_piece(piece):
return hash(tuple(piece))
def expand_pieces(pieces):
expanded = []
#[
# 332322396: [[(1,0), (0,-1)], [...]],
# 323200700000: [[(1,0), (0,-2)]]
#]
# Multimap because two different pieces can happen to have the same hash
expanded_hashes = defaultdict(list)
for piece in pieces:
for e in possible_expansions(piece):
exp = canonical(e)
is_new = True
if exp in expanded_hashes[hash_piece(exp)]:
is_new = False
for rotation in range(3):
exp = canonical(rotate_90_cw(exp))
if exp in expanded_hashes[hash_piece(exp)]:
is_new = False
if is_new:
expanded.append(exp)
expanded_hashes[hash_piece(exp)].append(exp)
return expanded
for i in range(2, n + 1):
pieces_of_size[i] = expand_pieces(pieces_of_size[i - 1])
print("Pieces with {} blocks: {}".format(i, len(pieces_of_size[i])))