Uber Interview Questions

Prepare for success with our curated collection of interview questions. Designed to help students practice and build confidence, these questions cover a range of topics and real-world scenarios to get you ready for your next interview.
  • DSA
  • LLD
  • HLD
Q1: Number of Islands II

Given a 2D matrix with 1’s and 0’s, exactly 2 islands exist in the matrix. Devise an algorithm to count and operate on these islands under constraints.

Design and implement a data structure for Least Recently Used (LRU) cache, supporting get and put operations in O(1) time.

Design a data structure to efficiently add numbers from a stream and retrieve the median at any time.

Given a list of words sorted lexicographically (but in an unknown language), figure out the order of characters in the language.

Given a reference of a node in a connected undirected graph, return a deep copy (clone) of the graph.

Given a non-empty array of integers, return the k most frequent elements.

  • Given: An array of integers nums and an integer limit.
  • Task: Return the size of the longest non-empty subarray such that the absolute difference between any two elements of this subarray is ≤ limit.
  • Approaches discussed:
    1. Brute-force (4 loops): Generate all subarrays and check the condition.
    2. Improved brute-force (3 loops): Avoid redundant checks.
    3. Further improved (2 loops): Track min/max for each window.
    4. Optimal (Sliding Window + Deque, O(n)): Maintain window min/max using two deques.
  • Input: Logs in format UserA-Shared-UserB-timestamp (UserA and UserB share a cab).
  • Version 1: For each log, return how many cabs are currently running (track number of connected components).
  • Version 2: For given logs, return the timestamp when all users are in one cab (all connected in a single set).
  • Description: Given an n×m grid with arrows pointing in different directions, calculate the minimum cost from the top-left to bottom-right, where moving in the direction of the arrow costs 0 and moving in any other direction costs 
  • Key Approaches:
    • DFS/Brute-force ( O(4x) O(4 x) time) Graph modeling with Dijkstra’s algorithm (BFS/priority queue, 0-1 BFS optimal)
  • Description: Given a number, find the next greater palindrome using a mirror and carry propagation approach.
  • Key Approaches:
    • Construct mirrored candidate, increment if needed, handle edge cases.
  • Description: Implement a class with methods put_element(k), get_element_count(k), and get_total_elements(), tracking expiry for elements after  t seconds.
  • Key Approaches:
    • Priority queue + hash map for expiry
    • Binary search on timestamps for efficiency
    • Must handle stale element cleanup efficiently

Given a list of airline tickets represented as pairs of departure and arrival airports [from, to], reconstruct the itinerary in order. All of the tickets form at least one valid itinerary. If there are multiple valid itineraries, return the itinerary that has the smallest lexical order when read as a single string.

  • Description: Given keys and their frequencies, find the optimal cost to construct the binary search tree such that the total cost of all searches is minimized. The cost of a BST is the sum of all keys multiplied by the depth of the keys.
  • Approach: Recursive solution and optimization using dynamic programming to avoid recomputation.

Given an array of integers, count how many elements have an odd number of occurrences of the digit 0 in their decimal representation.
Example:
Input: [10070]
Output: 3 (20 has one zero, 10 has one zero, 10070 has three zeros—each an odd count)

Given an array of non-negative integers representing sensor readings, find the digit (0-9) that appears most frequently across all readings written in decimal form. If multiple digits tie, return the smallest digit among them.

Given an array of integers where each integer represents the height of a structure, calculate the minimum total increment required to transform the array into either a strictly ascending or strictly descending stepwise sequence (where each element differs by exactly 1 from the previous) by only increasing heights (no decreases).

Given a 2D grid of bubbles denoted by integers (0 means empty), simulate one round of explosions and gravity as follows:

  • A bubble explodes if it has at least two adjacent bubbles of the same color (up, down, left, right).
  • Exploding bubbles trigger their adjacent same-colored bubbles to explode.
  • After explosion, bubbles above empty spaces fall down.
    Return the resulting grid after one round of explosions and gravity.
Q1. Multithreaded Code—Producer/Consumer, Thread Pools, etc

Write and design multithreaded code handling concurrency in object-oriented problems, touching on synchronization, thread safety, and extensibility.

Create a low-level design (classes, APIs) for a service converting long URLs into short, unique ones with encoding and redirection features.

  • Core functionalities:
    • Assign trains to platforms based on input.
    • Query which train is at a given platform at a specific time.
    • Query which platform a train is at, at a specific time.
  • Expectations:
    • Write runnable code (Java), use design patterns, and demonstrate extensibility.
    • Focus on scheduling, time-based queries, and mappings between trains/platforms.
    • Used a minHeap strategy for scheduling and also discussed random assigning.
    • Explain OOD decisions, and write only required variables/methods for clarity and brevity.
  • Description: Design and implement a set of classes based on a given set of use cases, encapsulating required functionality. Code should be extensible and well-structured, following proper OOP principles.
  • Focus: Class relationships, methods, data handling, and compliance with requirements.
  • Context: Conducted on CodeSignal platform for a 1-hour slot.
  • Problem Statement:
    Design a system to manage bookings for n meeting rooms. Requests come continuously with start and end times, and the system should allocate any available room for the requested time slot. If no rooms are available, the booking should be rejected or queued.
Q1. Design Uber's Ride-Matching System

Architect a scalable service to match nearby riders and drivers in real time, factoring in dynamic locations, surge pricing, ETA, and robustness at scale.

Design a service similar to Google Maps with efficient map data storage, live routing, address parsing, and traffic-aware pathfinding.

Design a scalable system for live real-time GPS updates for millions of users.

  • Description: Design and implement a publish-subscribe (pub-sub) messaging system that supports multiple publishers and subscribers. The system should simulate concurrency using Java threads with proper synchronization, thread safety, and message delivery guarantees.
  • Focus Areas:
    • Thread creation and management in Java.
    • Synchronization primitives (locks, wait/notify).
    • Message queues and buffering between publishers and subscribers.
    • Handling multiple producers and consumers concurrently.
  • Recommended Prep: Brush up on Java concurrency, thread synchronization, and concurrent data structures.
  • Focus Areas:
    • Location-based search (use GeoHashing & GeoIndexing).
    • API design for homepage and search results.
    • Schema design for Restaurants, Dishes, Orders.
    • DB choice and justification (SQL vs NoSQL).
    • Use of caching for homepage/search performance.
  • Metrics to handle:
    • Most ordered restaurant.
    • Most ordered dish.
    • Orders per restaurant.
  • Tools/Process:
    • Used design whiteboard for architecture diagrams.
    • Heavy focus on trade-offs, mistakes, and architecture critique.
  • Problem Statement:
    Design a system to handle bus ticket bookings. The system should allow users to search for buses on specific routes and dates, view available seats, book tickets, and handle cancellations. The system should ensure seat availability is accurately maintained and prevent double-bookings.
  • Key Requirements:
    • Maintain bus schedules with routes, timings, and seat capacity.
    • Support seat selection and booking transactions.
    • Handle concurrent booking requests and ensure data consistency.
    • Provide ticket cancellation and refund functionality.
    • Support user profiles and booking history.
  • Description: Design a system to create a real-time and batch dashboard for Uber driver location heatmaps for city analytics.
  • Key Points:
    • Real-time: Consume GPS events from Kafka, bucket by geohash, aggregate in Flink, cache in Redis.
    • Batch: Aggregate hourly data into Postgres for historical analytics.
    • Discussed aspects: Fault tolerance, scalability, API/data contracts, use of DynamoDB/Postgres, windowing, choice of cache store.
Q1. Discussion
  • Behavioral and manager round focused on:
    • Own coding practices, team and project ownership, and previous work impact.
    • Questions on good code, teamwork, and values.
    • Opportunity for candidate to ask about the team, role advancement, etc.

What does receiving a “waitlist” email after the Uber Online Assessment (OA) likely indicate, and how is it used in the selection process? Explain the scenarios in which candidates receive the waitlist email and what it means for further interview eligibility.

  • Context:
    • Candidates who solved all problems rapidly, those who solved fewer, and even some who did not attempt the OA at all received the same waitlist email.
    • Backend confirmation from an SDE-2 at Uber that this message is an automated (silent rejection) response, not an actual waitlist for interview rounds.
    • Only those who were moving forward to interviews received their scheduling/updates prior to the mass distribution of the waitlist messages.

 

  • Description: Discussion on impactful projects, technical and non-technical challenges faced, reasons for job change, future interests, and contribution to team/company.
  • Category: Behavioral (not DSA, LLD, HLD directly, but vital for bar raiser/managerial rounds).
  • Focus: Discuss past projects, ownership, technical and interpersonal challenges, motivation for role change, and future goals.
  • Key Points:
    • Situation, Task, Action, Result (STAR) method to structure answers.
    • Emphasize impact and learning.
    • Align past experience to the role’s demands and company values.
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