DoorDash Coding Interview Questions
32 DoorDash coding interview problems with full optimal solutions — 3 easy, 21 medium, 8 hard. Every problem ships with multiple approaches (brute-force first, then the optimal), complexity tables for each, company-specific tips on what an DoorDash interviewer values, and a FAQ section.
Showing 8 problems of 32
- #31hardfoundational
31. Sliding Window Maximum
Return the maximum value in each sliding window of size k — Doordash uses this deque pattern in their real-time demand forecasting: finding peak order rates over every rolling k-minute window to trigger Dasher surge dispatch.
- #32hardfoundational
32. Median of Two Sorted Arrays
Find the median of two sorted arrays in O(log(m+n)) — Doordash uses binary-search-on-sorted-partition thinking in their real-time delivery ETA percentile calculations that must run in microseconds across millions of rows.
- #42hardcompany favorite
42. Trapping Rain Water
Given an elevation map, compute how much rainwater would be trapped. DoorDash uses this as a hard-end array problem — they want the two-pointer O(1) space optimization, not just the precomputed-max arrays version.
3 free resourcesSolve → - #127hardfrequently asked
127. Word Ladder
Find the shortest transformation sequence from beginWord to endWord, changing one letter at a time and using only words in the dictionary. DoorDash leans on this for the BFS-on-implicit-graph pattern — they want to see the wildcard-key optimization on the adjacency lookup.
3 free resourcesSolve → - #212hardfrequently asked
212. Word Search II
Given a board and a list of words, return all words that can be formed by traversing adjacent cells. DoorDash uses this as a Trie + DFS combination — they want the trie-traversal speedup that beats naive per-word DFS.
3 free resourcesSolve → - #218hardfrequently asked
218. The Skyline Problem
Given a list of buildings (left, right, height), return the skyline as key points. DoorDash uses this for senior infrastructure rounds — the sweep-line + max-heap pattern shows up in surge-pricing and capacity-window problems.
3 free resourcesSolve → - #857hardfrequently asked
857. Minimum Cost to Hire K Workers
Hire exactly k workers so that each is paid at least their min-wage AND in proportion to their quality. Minimize total cost. DoorDash uses this for senior backend rounds — the dispatch and pricing problems have the same shape.
3 free resourcesSolve → - #1192hardfrequently asked
1192. Critical Connections in a Network
Given an undirected graph, return all bridges — edges whose removal disconnects the graph. DoorDash uses Tarjan's bridge-finding algorithm because logistics networks need to identify single points of failure in their routing infrastructure.
3 free resourcesSolve →
Related interview-prep guides
CodeSignal GCA for Tech Interviews in 2026: The Complete Guide
The CodeSignal General Coding Assessment is a 70-minute, four-task timed test scored on a 600 to 850 scale, used as a filter by Goldman Sachs, Capital One, Robinhood, Brex, and a growing list of tech and finance employers. This guide breaks down what it tests, how it scores, what it tracks during your session, and how a modern desktop setup pairs with it without showing up in proctored recordings.
CoderPad Live Coding Interview Guide (2026): What the Pad Tracks and How to Walk Through It Cleanly
CoderPad is the default live-coding environment for human-led technical interviews in 2026. Used by YC startups, FAANG-tier teams, and most of the tech mid-market. The pad records every keystroke, every paste event, every language switch, and offers an interviewer scrub-back feature most candidates never realize exists. This is what CoderPad tracks, how the live session compares to async assessments, and how a modern desktop AI setup pairs with it without showing up in the screen-share.
CodeInterview.io Live Coding Interview Guide (2026): What the Platform Tracks and How to Walk Through It Cleanly
CodeInterview.io is a browser-based collaborative live-coding platform. Think of it as a lighter-footprint alternative to CoderPad with an integrated video call, per-keystroke replay, and a drawing whiteboard. Smaller market share than CoderPad but shows up at a meaningful slice of YC startups and mid-market tech teams in 2026. This is what CodeInterview.io tracks, how its all-in-one workflow compares to CoderPad, and how a modern desktop AI setup pairs with it without showing up in the screen-share.