Heaps & Linked Lists
A min-heap gives you the smallest item that qualifies right now. A doubly linked list lets you take an item out of the middle and join its two neighbors in O(1). DoorDash expects you to build both by hand, and one problem here needs them together.
Each of the other two problems uses one of those structures, one as a class called one operation at a time and one as a ranked search that keeps its heap small.
Start with the problem that needs both structures. It comes up most often at the phone screen and has no LeetCode twin to memorize. The other two show up less. If the heap operations themselves are rusty, the Foundations heaps intro and top-K problems rebuild them from scratch.
DoorDashPremium lesson · Coding round
The 3 DoorDash problems are below.
- A Premium questionCoding · Hard · Signature problem
- A Premium questionCoding · Medium
- A Premium questionCoding · Medium
Each with hints, the follow-up and a tested solution.
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From 166 DoorDash reports, forum threads behind logins and write-ups in Chinese.
DoorDash interview guideKnow what DoorDash asks before you walk in.
30 coding · 5 system design · 21 behavioral questions
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