Doordash Coding & Algorithms Interview Questions
DoorDash Coding & Algorithms interview questions typically emphasize practical problem solving under time pressure, clear code, and product-minded tradeoffs. What’s distinctive is a bias toward realistic engineering tasks—scheduling, graph traversal, and array/string manipulation appear often—combined with an expectation that you communicate tradeoffs, test edge cases, and iterate quickly. Interviewers assess algorithmic thinking, correctness, complexity reasoning, and the ability to refactor or extend solutions when given follow-ups. Expect an initial technical screen followed by a loop of 2–4 interviews that blend live coding with behavioral and sometimes system-design conversations. For interview preparation, prioritize consistent timed practice on medium-to-hard problems, rehearse speaking your thought process, and run mock interviews in your target language and editor. Refresh core data structures, common patterns (DFS/BFS, two pointers, heaps, hash maps, dynamic programming), and time/space analysis. Finish prep by practicing end-to-end: state assumptions, outline an approach, code defensively, and validate with tests so you can both solve and clearly explain your solutions during the loop.

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Compute courier pay and implement load balancing
Problem 1: Compute courier (delivery driver) pay You are given a sequence of delivery-related events for a courier during a day. Your task is to compu...
Minimize batches and allocate riders by time
Coding prompts (same interview round) 1) Minimum number of batches for time points You are given a list of event time points (integers), e.g. [1, 3, 5...
Compute cart total with best promotion
Assume you are implementing a checkout price calculator for an online shopping cart. You are given: - A list of items in the cart. Each item has: - ...
Compute dasher pay with peak-hour query
Problem: Dasher pay calculation + peak-hour earnings You are given historical delivery records for a driver (“dasher”). Each record contains: - start_...
Count changed nodes between two menu trees
You maintain a merchant menu as a rooted tree. Each node represents a menu item/category and has: - key (string, unique among siblings) - value (integ...
Implement round-robin load balancer
Implement a load balancer that distributes incoming requests across N backend servers in strict round-robin order. Requirements: ( 1) Support addServe...
Debug round-robin, DashMap, and simple cache
You are given a service that routes requests to a list of nodes, each marked as either available or unavailable. The pickNode() function is intended t...
Find longest common ordered restaurant list
You have two delivery drivers who each have a pickup plan represented as a list of restaurant IDs (strings). Because there is only one car, the combin...
Implement and compare round-robin and consistent hashing
Implement a round-robin load balancer that selects among service nodes, skipping unavailable nodes and wrapping around correctly. Fix typical pitfalls...
Debug a driver assignment bug
Given a service that selects the best delivery driver ("dasher") for an order, users report incorrect assignments. With a provided codebase and failin...
Implement dasher active-time calculator
Implement a function that, given a dasherId, a local pay-period interval [startLocalDateTime, endLocalDateTime), and a list of order events of the for...
Implement minimum window substring with counts
Implement min_window_with_counts(s, t) Task Write a function: - min_window_with_counts(s: str, t: str) -> tuple[int, int] that returns the inclusive (...
Debug and refactor a legacy module
Given a legacy module named DasherPicker and a failing test suite, systematically debug and refactor the code while following a provided review checkl...
Find the nearest city sharing axis
You are given N cities, each with a unique name and integer coordinates (x, y). For any query city, return the nearest city that shares either the sam...
Debug using logs and allocate tasks
You inherit a service where unit tests pass locally, but production logs show intermittent errors. Without a debugger, outline a step-by-step debuggin...
Implement image carousel with comments and upvotes
Implement an image carousel that supports: 1) cycling forward/backward and autoplay with a configurable interval; 2) a per-image comment thread with c...
Find closest value to a target in a BST
Problem Given the root of a binary search tree (BST) and a floating-point number target, return the value in the BST that is closest to target. If the...
Design dynamic connectivity with alive nodes
Design a data structure to maintain an undirected graph of N nodes, where each node has a boolean 'alive' flag. Support the following operations effic...
Compute Differences Between Catalog Trees
You are given two rooted catalog trees. Each node has a unique string key among its siblings and an associated value. Compare the two trees and return...
Find nearest courier for each customer
Given two sets of 2D points: customers C = {c1..cn} and active couriers D = {d1..dm}, return for every customer the nearest courier by geographic dist...