20+ AntWalk Interview Questions and Answers

An Android photo viewing app with a list of images from disk, one taking half the screen.

• Use RecyclerView to display the list of images

• Use a custom adapter to bind the images to the RecyclerView

• Use a GridLayoutManager with span count of 2 to achieve the half-screen effect

• Load images from disk using a library like Glide or Picasso

• Implement click listeners to handle item selection and display the selected image

Rearrange the nodes of a singly linked list in a specific order without altering the data of the nodes.

• Use two pointers to split the linked list into two halves.

• Reverse the second half of the linked list.

• Merge the two halves alternately to rearrange the nodes.

• Ensure to handle cases with odd and even number of nodes separately.

• Example: For input 1 -> 2 -> 3 -> 4 -> 5, the output should be 1 -> 5 -> 2 -> 4 -> 3.

Given a string of consecutive nonnegative integers without separators, find the missing integer.

• Iterate through all possible splits of the string and check if the sequence is valid

• If the sequence is valid, return the missing integer

• Handle cases where there are multiple missing integers or the string is invalid

Design a Least Recently Used (LRU) cache data structure that supports get and put operations with capacity constraint.

• Implement a doubly linked list to keep track of the order of keys based on their recent usage.

• Use a hashmap to store key-value pairs for quick access and update.

• When capacity is reached, evict the least recently used item before inserting a new item.

• Update the order of keys in the linked list whenever a key is accessed or updated.

Design a screen to show 10 nearest restaurants in a list with uninterrupted scrolling.

• Use a RecyclerView to display the list of restaurants

• Implement a custom adapter to populate the data in the list

• Use a location service to get the user's current location

• Sort the restaurants based on their distance from the user's location

• Load more restaurants as the user scrolls to the end of the list

Check if a permutation of a string can form a palindrome.

• Create a frequency map of characters in the string.

• Check if at most one character has an odd frequency.

• If yes, return True; otherwise, return False.

To search for contacts with duplicate names or numbers, iterate through the list and compare each contact's name and number with the search term.

• Iterate through the list of contacts

• Compare the search term with each contact's name and number

• Return the contacts that match the search term

To transfer the Ball object from one thread to another, we can use Handler or AsyncTask.

• Use Handler to post a Runnable to the main thread's message queue

• Use AsyncTask to perform background operations and update the UI on the main thread

• Pass the Ball object as a parameter or use a shared variable between threads

To create my own HashMap, I would use an array of linked lists to handle collisions and implement key-value pairs using a hash function.

• Create an array of linked lists to store the key-value pairs

• Implement a hash function to generate an index for each key

• Handle collisions by adding elements to the linked list at the corresponding index

• Support operations like put(key, value), get(key), and remove(key)

Given an array of natural numbers in random order, find the first missing natural number.

• Sort the array in ascending order

• Iterate through the sorted array and compare each element with its index

• If the element is not equal to its index + 1, return the missing number

• If all elements are in order, return the next natural number after the last element

Use a Handler or AsyncTask to pass a Java object between threads.

• Use a Handler to send messages containing the object from one thread to another.

• Use AsyncTask to perform background tasks and update UI with the object on the main thread.

Looper/handlers allow passing objects between threads in Android.

• Looper is a message loop that runs in a thread and processes messages from a message queue.

• Handlers are used to send messages to the message queue of a looper.

• When an object is passed from one thread to another using a handler, it is encapsulated in a message and added to the receiving thread's message queue.

• The receiving thread's looper then processes the message and delivers it to the handler's callback method...read more

Use a thread pool to handle parallel API calls efficiently.

• Implement a thread pool to manage multiple threads for downloading images concurrently.

• Use a caching mechanism to store downloaded images and avoid redundant API calls.

• Consider using a priority queue to prioritize important images for download.

• Implement a mechanism to cancel or pause ongoing downloads if needed.

• Optimize network requests by batching multiple requests together.

A weather app that displays images for different weather conditions, taking care of half downloaded images and minimizing data consumption.

• Implement image caching to store downloaded images locally

• Check if the image is already downloaded before making a network request

• Use a progress bar to indicate the download status of the image

• Handle cases where the download is interrupted or incomplete

• Implement a mechanism to resume the download from where it left off

• Optimize image loadin...read more

Different launch modes for activities in Android control how the activity is launched and how it interacts with the existing activities in the back stack.

• Standard: The default launch mode where a new instance of the activity is created every time it is launched.

• SingleTop: If the activity is already at the top of the back stack, it will not be recreated and onNewIntent() will be called instead.

• SingleTask: The activity will have a unique instance in the back stack, and if it is...read more

Deep links are URLs that take users directly to specific content within an app, while app links are URLs that open an app if it's installed, or redirect to a website if not.

• Deep links are used to navigate users to a specific location within an app, bypassing the home screen.

• App links are URLs that can open an app if it's installed on the device, or redirect to a website if the app is not installed.

• Deep links require specific handling in the app to properly navigate to the des...read more

Inter-Process Communication (IPC) mechanisms in Android OS allow different processes to communicate with each other.

• Binder: High-performance mechanism for IPC between processes in Android. Used for communication between system services and applications.

• Intent: Used for communication between components within the same application or between different applications.

• Content Providers: Allow different applications to share data through a common interface.

• Broadcast Receivers: Used ...read more

Android components like Recycler View, View Model, ANR are essential for building robust Android applications.

• Recycler View: Efficient way to display large data sets by recycling views as they scroll off the screen.

• View Model: Manages UI-related data in a lifecycle-conscious way, surviving configuration changes.

• ANR (Application Not Responding): Dialog shown to the user when the main thread of an app is blocked for too long.

• Understanding how these components work internally is...read more

ImageDownloader efficiently handles parallel API calls.

• Use a thread pool to manage parallel API calls.

• Implement caching to avoid redundant API calls.

• Use a priority queue to prioritize image downloads.

• Optimize network requests by using HTTP/2 or multiplexing.

• Consider using a library like Picasso or Glide for image loading and caching.

CyclicBarrier in Java is a synchronization aid that allows a set of threads to wait for each other to reach a common barrier point.

• CyclicBarrier is initialized with a count of the number of threads that must invoke await() before the barrier is tripped.

• Threads wait at the barrier until all threads have invoked await(), then the barrier is released.

• Once the barrier is tripped, it can be reused for subsequent synchronization points.

• CyclicBarrier can be used in scenarios where m...read more

Deep linking in Android allows users to navigate directly to specific content within an app.

• Deep linking is achieved by defining intent filters in the app's manifest file.

• The intent filter specifies the URL scheme and host that the app can handle.

• When a deep link is clicked, Android checks if any app can handle the URL and prompts the user to choose.

• The chosen app receives the deep link data in the intent's data field.

• Deep linking can be used to open specific screens, perform...read more

IntentService is a subclass of Service that can handle asynchronous requests on the main thread.

• IntentService is used for handling long-running operations in the background without blocking the main thread.

• It is started with an Intent and runs in a separate worker thread.

• Once the task is completed, the IntentService stops itself automatically.

• It is commonly used for tasks like downloading files, syncing data, or performing network operations.

Launch mode determines how an activity is launched and how it behaves in the task stack.

• Standard: Creates a new instance of the activity on each launch.

• SingleTop: Reuses the existing instance if it's already at the top of the stack.

• SingleTask: Creates a new task and places the activity at the root of the task.

• SingleInstance: Creates a new task and places the activity as the only one in the task.

IPC (Inter-Process Communication) methods in Android allow communication between different processes.

• Binder: Android's native IPC mechanism, used for communication between processes.

• Intents: Used for communication between components within the same application or between different applications.

• Content Providers: Allow sharing data between applications using a common interface.

• Broadcasts: Used for asynchronous communication between components within an application or between d...read more