Sudoku (Game.java)

package org.example.sudoku;
 
import android.app.Activity;
import android.app.Dialog;
import android.os.Bundle;
import android.util.Log;
import android.view.Gravity;
import android.widget.Toast;
 
public class Game extends Activity {
   private static final String TAG = "Sudoku";
 
   public static final String KEY_DIFFICULTY = "org.example.sudoku.difficulty";
   public static final int DIFFICULTY_EASY = 0;
   public static final int DIFFICULTY_MEDIUM = 1;
   public static final int DIFFICULTY_HARD = 2;
 
   private int puzzle[] = new int[9 * 9];
 
   private PuzzleView puzzleView;
 
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      Log.d(TAG, "onCreate");
 
      int diff = getIntent().getIntExtra(KEY_DIFFICULTY, DIFFICULTY_EASY);
      puzzle = getPuzzle(diff);
      calculateUsedTiles();
 
      puzzleView = new PuzzleView(this);
      setContentView(puzzleView);
      puzzleView.requestFocus();
   }
 
   /** Open the keypad if there are any valid moves */
   protected void showKeypadOrError(int x, int y) {
       int tiles[] = getUsedTiles(x, y);
       if(tiles.length == 9) {
           Toast toast = Toast.makeText(this, R.string.no_moves_label, Toast.LENGTH_SHORT);
           toast.setGravity(Gravity.CENTER, 0, 0);
           toast.show();
       } else {
           Log.d(TAG, "showKeypad: used=" + toPuzzleString(tiles));
           Dialog v = new Keypad(this, tiles, puzzleView);
           v.show();
       }
   }
 
   /** Change the tile only if it's a vaoid move */
   protected boolean setTileIfValid(int x, int y, int value) {
       int tiles[] = getUsedTiles(x, y);
       if(value != 0) {
           for(int tile : tiles) {
               if(tile == value) return false;
           }
       }
       setTile(x, y, value);
       calculateUsedTiles();
       return true;
   }
 
   /** Cache of used tiles */
   private final int used[][][] = new int[9][9][];
 
   /** Return cached used tiles visible from the given coords */
   protected int[] getUsedTiles(int x, int y) {
       return used[x][y];
   }
 
   /** Compute the two dimensional array of used tiles */
   private void calculateUsedTiles() {
       for(int x = 0; x < 9; x++) {
           for(int y = 0; y < 9; y++) {
               used[x][y] = calculateUsedTiles(x, y);
               // Log.d(TAG, "used[" + x + "][" + y + "] = "
               // + toPuzzleString(used[x][y]));
           }
       }
   }
 
   /** Compute the used tiles visible from this position */
   private int[] calculateUsedTiles(int x, int y) {
       int c[] = new int[9];
       // horizontal
       for(int i = 0; i < 9; i++) {
           if(i == y) continue;
           int t = getTile(x, i);
           if(t != 0) c[t - 1] = t;
       }
       // vertical
       for(int i = 0; i < 9; i++) {
           if(i == x) continue;
           int t = getTile(i, y);
           if(t != 0) c[t - 1] = t;
       }
       // same cell block
       int startx = (x / 3) * 3;
       int starty = (y / 3) * 3;
       for(int i = startx; i < startx + 3; i++) {
           for(int j = starty; j < starty + 3; j++) {
               if(i == x && j == y) continue;
               int t = getTile(i, j);
               if(t != 0) c[t - 1] = t;
           }
       }
       // compress
       int nused = 0;
       for(int t : c) {
           if(t != 0) nused++;
       }
       int c1[] = new int[nused];
       nused = 0;
       for(int t : c) {
           if(t != 0) c1[nused++] = t;
       }
       return c1;
   }
 
   private final String easyPuzzle =
       "360000000004230800000004200" +
       "070460003820000014500013020" +
       "001900000007048300000000045";
   private final String mediumPuzzle =
       "650000070000506000014000005" +
       "007009000002314700000700800" +
       "500000630000201000030000097";
   private final String hardPuzzle =
       "009000000080605020501078000" +
       "000000700706040102004000000" +
       "000720903090301080000000600";
 
   /** Given a difficulty level, come up with a new puzzle */
   private int[] getPuzzle(int diff) {
       String puz;
       // TODO: Continue last game
       switch(diff) {
       case DIFFICULTY_HARD:
           puz = hardPuzzle;
           break;
       case DIFFICULTY_MEDIUM:
           puz = mediumPuzzle;
           break;
       case DIFFICULTY_EASY:
       default:
           puz = easyPuzzle;
           break;           
       }
       return fromPuzzleString(puz);
   }
 
   /** Convert an array into a puzzle string */
   static private String toPuzzleString(int[] puz) {
       StringBuilder buf = new StringBuilder();
       for(int element : puz) {
           buf.append(element);
       }
       return buf.toString();
   }
 
   /** Convert a puzzle string into an array */
   static protected int[] fromPuzzleString(String string) {
       int[] puz = new int[string.length()];
       for(int i = 0; i < puz.length; i++) {
           puz[i] = string.charAt(i) - '0';
       }
       return puz;
   }
 
   /** Return the tile at the given coordinates */
   private int getTile(int x, int y) {
       return puzzle[y * 9 + x];
   }
 
   /** Change the tile at the given coordinates */
   private void setTile(int x, int y, int value) {
       puzzle[y * 9 + x] = value;
   }
 
   /** Return a string for the tile at the given coordinates */
   protected String getTileString(int x, int y) {
       int v = getTile(x, y);
       if(v == 0) return "";
       else return String.valueOf(v);
   }
 
   @Override
   protected void onResume() {
       super.onResume();
       Music.play(this, R.raw.game);
   }
 
   @Override
   protected void onPause() {
       super.onPause();
       Music.stop(this);
   }
}