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 21 problems of 32
- #24mediumfoundational
24. Network Delay Time
Find the minimum time a signal takes to reach all nodes in a weighted graph — Doordash maps this directly to Dijkstra delivery-routing: how long until every zone gets its first Dasher signal.
- #25mediumfoundational
25. Meeting Rooms II
Find the minimum number of concurrent resources to cover all intervals — Doordash applies this exact pattern to Dasher shift scheduling: how many active Dashers are needed at peak overlap?
- #26mediumfoundational
26. Design Hit Counter
Build a counter that returns hits within a rolling 5-minute window — Doordash uses this real-time design pattern in their order-surge detection and Dasher-availability rate-limiting infrastructure.
- #27mediumfoundational
27. Jump Game
Determine if you can traverse an array by jumping up to each cell's value — Doordash uses this greedy reachability pattern when modeling whether a Dasher can cover consecutive delivery zones given variable driving ranges.
- #28mediumfoundational
28. Coin Change
Find the fewest coins to reach an exact amount — Doordash uses this DP pattern for delivery batch optimization: the minimum number of courier trips to fulfill an order backlog of a given volume.
- #29mediumfoundational
29. Subarray Sum Equals K
Count contiguous subarrays whose values sum to a target — Doordash applies this prefix-sum hash-map technique to detect delivery batches that hit an exact revenue threshold in a stream of order values.
- #30mediumfoundational
30. Clone Graph
Deep-clone an undirected connected graph — Doordash uses this graph-traversal pattern when replicating delivery zone topology across regional data centers for failover and load balancing.
- #15mediumfrequently asked
15. 3Sum
Given an integer array, return all unique triplets that sum to zero. DoorDash uses 3Sum as the canonical 'sort + two-pointer' problem — they want clean dedupe logic and the O(n^2) bound.
3 free resourcesSolve → - #146mediumcompany favorite
146. LRU Cache
Design a cache that evicts the least recently used key when full. DoorDash asks this for backend SWE loops because logistics systems lean on LRU eviction for hot order/driver lookups — they want both get and put in O(1).
3 free resourcesSolve → - #207mediumfrequently asked
207. Course Schedule
Given courses and prerequisites, determine if you can finish all courses. DoorDash uses this to test cycle detection in directed graphs — they want either DFS with white/gray/black coloring or Kahn's BFS topological sort.
3 free resourcesSolve → - #210mediumfrequently asked
210. Course Schedule II
Given courses with prerequisites, return a valid ordering or an empty array if no ordering exists. DoorDash uses this as the Course Schedule follow-up — same cycle detection but you also output the topological order.
3 free resourcesSolve → - #215mediumcompany favorite
215. Kth Largest Element in an Array
Find the kth largest element in an unsorted array. DoorDash uses this to test heap fluency AND the average-O(n) quickselect — they want both verbally, with quickselect coded if time allows.
3 free resourcesSolve → - #277mediumfrequently asked
277. Find the Celebrity
Given n people and a knows(a, b) API, find the celebrity — someone known by everyone but who knows nobody. DoorDash uses this to test whether you spot the O(n) elimination trick instead of the O(n^2) brute-force matrix check.
3 free resourcesSolve → - #340mediumfrequently asked
340. Longest Substring with At Most K Distinct Characters
Given a string and an integer k, return the length of the longest substring with at most k distinct characters. DoorDash uses this as a sliding-window template — they want a clean expand-shrink pattern with a count map.
3 free resourcesSolve → - #347mediumfrequently asked
347. Top K Frequent Elements
Given an integer array and k, return the k most frequent elements. DoorDash uses this as a hash + heap warm-up — they want you to discuss both the heap-based O(n log k) and the bucket-sort O(n) approaches.
3 free resourcesSolve → - #380mediumfrequently asked
380. Insert Delete GetRandom O(1)
Design a data structure that supports insert, remove, and getRandom each in O(1) average. DoorDash uses this for backend rounds — they want the swap-with-last-then-pop trick that combines a hash map and an array.
3 free resourcesSolve → - #416mediumfrequently asked
416. Partition Equal Subset Sum
Return true if the array can be partitioned into two subsets with equal sums. DoorDash uses this as a 0/1 knapsack disguised as a partition problem — they want the bottom-up DP that uses a boolean array.
3 free resourcesSolve → - #528mediumfrequently asked
528. Random Pick with Weight
Given an array of weights, implement pickIndex() that returns an index in proportion to its weight. DoorDash uses this for backend rounds — weighted random sampling shows up in load balancing, driver assignment, and A/B test bucketing.
3 free resourcesSolve → - #621mediumfrequently asked
621. Task Scheduler
Given tasks and a cooldown n, return the minimum CPU intervals needed. DoorDash uses this for backend scheduling rounds — the same shape appears in courier dispatch with cooldowns between assignments.
3 free resourcesSolve → - #692mediumfrequently asked
692. Top K Frequent Words
Given an array of words and k, return the k most frequent strings sorted by frequency descending, then lexicographically ascending on ties. DoorDash uses this as the Top K Frequent Elements follow-up with the tie-breaker twist that catches careless candidates.
3 free resourcesSolve → - #1091mediumfrequently asked
1091. Shortest Path in Binary Matrix
Find the length of the shortest clear path from top-left to bottom-right in a 0/1 grid, moving in 8 directions. DoorDash uses this as the canonical BFS-on-grid question — they want a clean queue with 8-directional moves, NOT DFS.
3 free resourcesSolve →
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