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object Stats {
  
  def simpleMovingAverage1(xs: List[Dobule], w: Int): List[Double] = {
    xs sliding w map (_.sum) map (_ / w) toList
  }
  
  def simpleMovingAverage2(xs: List[Double], w: Int): List[Double] = {
    def movingSum(xs: List[Double], w: Int): List[Double] = w match {
      case 0 => throw new IllegalArgumentException("Window size must be greater than 0")
      case 1 => xs

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object Strings {
  
  def isAnagram(s1: String, s2: String): Boolean = {
    if (s1 == null || s2 == null || s1.length != s2.length) return false
    s1.zip(s2).foldLeft(0){ case (result, (left, right)) => result ^ (left ^ right) } == 0
  }
  
  def isAnagram2(s1: String, s2: String): Boolean = {
    val m1 = s1 groupBy(c => c) mapValues(_.length)
    val m2 = s2 groupBy(c => c) mapValues(_.length)

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public class ViewUtils {
  private static final String TAG = "ViewUtils";

  public static void dumpViewHierarchy(ViewGroup root) {
    final Set<String> visitedResNames = new HashSet<>();
    walkNode(root, root.getResources(), visitedResNames);
  }

  private static void walkNode(ViewGroup node, Resources resources, Set<String> visitedResNames) {
    final String resName = getResourceName(node.getId(), resources);

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public abstract class UIHandler<T extends Activity> extends Handler {
  private final WeakReference<T> mRef;
  
  public UIHandler(T a) {
    mRef = new WeakReference<>(a);
  }

  @Override
  public void handleMessage(Message msg) {
    final T a = mRef.get();

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public class ImageFetcherActivity extends AppCompactActivity {
    class WorkerThread extends Thread {
        void fetchImage(String url) {
            // network logic to create and execute request
            handler.post(new Runnable() {
                @Override
                public void run() {
                    imageView.setImageBitmap(image);
                }
            });

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public class ImageFetcherAltActivity extends AppCompactActivity {
    class WorkerThread extends Thread {
        void fetchImage(String url) {
            handler.sendEmptyMessage(MSG_SHOW_LOADER);
            // network call to load image
            handler.obtainMessage(MSG_SHOW_IMAGE, imageBitmap).sendToTarget();
        }
    }
    
    class UIHandler extends Handler {

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static class UIHandler extends Handler {
    private final WeakReference<ImageFetcherActivity> mActivityRef;
    
    UIHandler(ImageFetcherActivity activity) {
        mActivityRef = new WeakReference(activity);
    }
    
    @Override
    public void handleMessage(Message msg) {
        final ImageFetcherActivity activity = mActivityRef.get();

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static class UIHandler extends Handler {
    private final WeakReference<ImageFetcherActivity> mActivityRef;
    
    UIHandler(ImageFetcherActivity activity) {
        mActivityRef = new WeakReference(activity);
    }
    
    @Override
    public void handleMessage(Message msg) {
        final ImageFetcherActivity activity = mActivityRef.get();

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public class MainActivity extends AppCompatActivity {
    private static final String IMAGE_URL = "https://www.android.com/static/img/android.png";

    private static final int MSG_SHOW_PROGRESS = 1;
    private static final int MSG_SHOW_IMAGE = 2;

    private ProgressBar progressIndicator;
    private ImageView imageView;
    private Handler handler;

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public class MainActivity extends AppCompatActivity {
    private static final String TAG = "Ping";

    private Handler handler;

    class PingHandler extends Handler {
        @Override
        public void handleMessage(Message msg) {
            Log.d(TAG, "Ping message received");
        }