Uber SDE Interview Questions and Answers

Find k closest points to origin from a set of 2D points.

• Calculate distance of each point from origin using distance formula

• Sort the points based on distance in ascending order

• Return first k points from the sorted list

iOS manual memory management requires developers to manually allocate and deallocate memory for objects.

• Developers must manually allocate memory for objects using methods like alloc and init.

• Developers must also manually deallocate memory for objects using methods like release.

• Failure to properly manage memory can lead to memory leaks and crashes.

• ARC (Automatic Reference Counting) was introduced in iOS 5 to automate me...read more

Program to print powerset of a given set

• Create an empty list to store subsets

• Loop through all possible binary numbers from 0 to 2^n-1 where n is the length of the set

• For each binary number, convert it to binary and use the 1's as indices to select elements from the set

• Add the selected elements to the list of subsets

• Return the list of subsets

Convert Roman numerals to integer in O(n) time

• Create a dictionary to map Roman numerals to integers

• Iterate through the string from right to left

• If the current numeral is less than the previous, subtract it from the total

• Else, add it to the total

• Return the total

Given a list of numbers and symbols, provide an expression that evaluates to a target number.

• Use recursion to try all possible combinations of numbers and symbols

• Check for division by zero and negative numbers

• Return False if no expression evaluates to the target number

Solve for x in a given expression with single variable.

• Simplify the expression by applying the distributive property and combining like terms.

• Isolate the variable term on one side of the equation and the constant terms on the other side.

• Solve for x by dividing both sides of the equation by the coefficient of the variable term.

• Check the solution by substituting the value of x back into the original equation.

• In this case...read more

Given a hashmap M and an input string S, return an array of all possible mutations of S using M's substitutes.

• Iterate through each character in S and get its substitutes from M

• Use recursion to generate all possible combinations of substitutes for each character

• Time complexity: O(n^m) where n is the average number of substitutes per character and m is the length of S

• Space complexity: O(n^m) due to the number of possible...read more

Facebook implements graph search by indexing user data and using natural language processing.

• Facebook indexes user data to create a graph of connections and relationships.

• Natural language processing is used to interpret user queries and return relevant results.

• Graph search allows users to search for specific information within their network, such as 'friends who like hiking'.

Facebook chat is a real-time messaging service that allows users to communicate with each other through the Facebook website or mobile app.

• Facebook chat uses XMPP (Extensible Messaging and Presence Protocol) to enable real-time communication between users.

• Messages are sent and received through Facebook's servers, which act as intermediaries between users.

• Users can see when their friends are online and available to chat...read more

Facebook stores likes/dislikes as data points in their database.

• Likes and dislikes are stored as separate data points.

• Each like/dislike is associated with a unique ID for the post or comment.

• The data is stored in Facebook's database and can be accessed through their API.

• Likes/dislikes can also be used to personalize a user's newsfeed.

• Facebook also uses likes/dislikes to gather data for targeted advertising.

Status updates can be implemented through various methods such as push notifications, real-time updates, and periodic polling.

• Use push notifications to instantly update users on important changes.

• Implement real-time updates using websockets or server-sent events for a seamless user experience.

• Periodically poll the server for updates using AJAX or other similar technologies.

• Provide a clear and concise interface for user...read more

A timeline/newsfeed can be implemented using a combination of algorithms and data structures.

• Use a database to store user activity data

• Implement an algorithm to sort the data by time

• Use pagination to limit the number of items displayed at once

• Include options for filtering and searching

• Consider using caching to improve performance

Adding someone as a friend allows you to connect with them on the platform and see their updates.

• When you add someone as a friend, they receive a notification and can choose to accept or decline your request.

• Once they accept your request, you can see their updates and they can see yours.

• You can also message each other and tag each other in posts.

• Adding someone as a friend does not give them access to your personal info...read more

Hadoop is a distributed computing framework used for storing and processing large datasets.

• Hadoop is based on the MapReduce programming model.

• It allows for parallel processing of large datasets across multiple nodes.

• Hadoop consists of two main components: HDFS for storage and MapReduce for processing.

• It is commonly used for big data analytics, machine learning, and data warehousing.

• Examples of companies using Hadoop in

FB messages work by allowing users to send and receive text, images, videos, and other media through the Facebook platform.

• Messages can be sent to individuals or groups of people.

• Users can also send voice messages and make voice and video calls through the messaging feature.

• Messages can be archived or deleted, and users can also choose to ignore or block certain senders.

• Facebook uses end-to-end encryption to protect th...read more

FB Mail is a messaging service that allows Facebook users to send and receive messages from other users.

• FB Mail is integrated into the Facebook platform and can be accessed through the Messenger app or website.

• Users can send messages to individuals or groups, and can also attach files, photos, and videos.

• FB Mail also includes features such as message requests, message filtering, and message archiving.

• Messages can be se...read more

Find the second largest element in an array.

• Sort the array and return the second last element

• Iterate through the array and keep track of the two largest elements

• Use a priority queue to find the second largest element

Given a sorted array with repeated elements, find the occurrence of a given element using binary search.

• Use binary search to find the first occurrence of the element

• Use binary search to find the last occurrence of the element

• Calculate the occurrence by subtracting the indices of the last and first occurrences and adding 1

Implement a data structure and algorithm to print all files in a directory, including sub-directories.

• Use an n-ary tree or stack to represent the directory structure

• Implement a BFS or DFS algorithm to traverse the directory and print files

• Handle sub-directories recursively

• Consider using a queue or stack to keep track of directories to visit

Print a matrix diagonally.

• Start from the top left corner and print the diagonal elements

• Move down and right to print the next diagonal

• Repeat until all diagonals are printed

DFS is a traversal algorithm used to visit all nodes of a tree or graph. It can be applied to binary as well as n-ary trees.

• DFS stands for Depth First Search.

• In DFS, we start from the root node and visit its children recursively until we reach a leaf node.

• There are two types of DFS: Preorder (root, left, right) and Postorder (left, right, root).

• DFS can be implemented using recursion or a stack data structure.

• Example: I...read more

To find the top 10 selling products, sort the products by their sales count in descending order and select the first 10.

• Sort the products by their sales count in descending order

• Select the first 10 products from the sorted list

Design a valet parking lot with ticket assignment and car retrieval using best fit and nearest distance.

• Create a parking lot with designated spots for each size of car

• Assign a ticket to the customer upon entry and record the spot number

• Retrieve the car by searching for the nearest available spot of the appropriate size

• Use best fit algorithm to minimize empty spots

• Implement a system for payment upon exit

Find total possible valid unique combinations of given number of pairs of parenthesis without duplicity.

• Use recursion to generate all possible combinations

• Check for validity of each combination using a stack

• Use a set to avoid duplicity

Construct a binary tree from in-order traversal with nodes greater than left and right child.

• The root node will be the maximum value in the in-order traversal

• Recursively construct the left and right subtrees using the left and right portions of the in-order traversal

• Repeat until all nodes are added to the tree

An algorithm to find top 10 trending words inserted by users in sites like Twitter.

• Collect a large dataset of tweets

• Tokenize the tweets into individual words

• Remove stop words and punctuation

• Count the frequency of each word

• Sort the words by frequency in descending order

• Select the top 10 words

Find the first occurrence of 1 in a sorted binary array.

• Use binary search to find the first occurrence of 1.

• If the mid element is 1, check if it's the first occurrence or if the element before it is 0.

• If the mid element is 0, search in the right half of the array.

• If the mid element is 1 and the element before it is also 1, search in the left half of the array.

Remove duplicates from a string in O(n) without using hash

• Use an array of boolean values to keep track of characters already seen

• Iterate through the string and mark characters as seen in the array

• If a character has already been seen, remove it from the string

Find the first occurrence of 1 in a sorted infinite binary tree.

• Use binary search to traverse the tree.

• If the current node is 1, check if its left child is also 1. If yes, move to the left subtree, else return the current node.

• If the current node is 0, move to the right subtree.

• Repeat until the first occurrence of 1 is found or the tree is exhausted.