fix block contraint

app/src/main/java/sudoku/Block.java

@@ -23,4 +23,12 @@ public class Block {
 		this.cells.add(newCell);
 	}
 
+	public boolean containsSymbol(int symbolIndex) {
+		for (Cell cell : getCells()) {
+			if (cell.getSymbolIndex() == symbolIndex)
+				return true;
+		}
+		return false;
+	}
+
 }

app/src/main/java/sudoku/constraint/BlockConstraint.java

@@ -1,22 +1,14 @@
 package sudoku.constraint;
 
 import sudoku.Block;
-import sudoku.MutableCell;
 import sudoku.Sudoku;
 
 public class BlockConstraint implements IConstraint{
 
 	@Override
 	public boolean canBePlaced(final Sudoku s, int x, int y, int newSymbolIndex) {
-
-		/*
-		boolean result = true;
-		for (Block block : s.getCell(x, y).getBlockContainers()) {
-			result = result && (!block.getCells().contains(new MutableCell(newSymbolIndex)));
-		}
-		 */
-		return !s.getBlocks().getCells().contains(new MutableCell(newSymbolIndex));
-
+		Block bloc = s.getCell(x, y).getBlock();
+		return !bloc.containsSymbol(newSymbolIndex);
 	}
 
 }