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DoorDash·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
May 2026

Summary

DoorDash software engineer round with a problem I'd never seen before. Had to code it live which added some pressure, but the problem itself was actually interesting once I wrapped my head around it.

Questions Asked (1)

Q1

Given three arrays representing chef skill levels, dish difficulty levels, and dish profits (all the same length), assign each chef to exactly one dish such that a chef can only cook a dish if their skill level meets the dish difficulty. Multiple chefs can be assigned to the same dish. Maximize the total profit.

Algorithms & Data Structures
Author's notes

Never ran into this type before.

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AI HintsAI Generated

Suggested Approach

Sort the dishes by difficulty and compute a prefix maximum of profits to quickly find the best profit for any skill level. Then for each chef, binary search the sorted difficulties to find the highest difficulty they can handle, and add the corresponding maximum profit. This greedy approach works because each chef's assignment is independent and we always pick the best available dish for their skill.

Pro tip: Clarify that multiple chefs can be assigned to the same dish, so there's no need to track dish usage. Also, mention that if a chef cannot cook any dish, they contribute 0 profit, and the algorithm should handle that gracefully.

1. Understand the problem and constraints

Restate the problem: each chef must be assigned to exactly one dish they can cook (skill >= difficulty), multiple chefs can share a dish, and we want to maximize total profit. Confirm edge cases like no feasible dish for a chef.

2. Preprocess dishes for efficient lookup

Sort dishes by difficulty. Compute a prefix maximum array where for each dish, we store the maximum profit among all dishes with difficulty <= current difficulty. This allows O(1) retrieval of the best profit for any skill threshold.

3. Process each chef

For each chef, binary search the sorted difficulties to find the largest difficulty <= chef's skill. If found, add the corresponding prefix maximum profit to the total; otherwise, add 0.

4. Analyze complexity and discuss optimizations

Time complexity: O((n + m) log n) where n is number of dishes and m is number of chefs, due to sorting and binary searches. Space complexity: O(n) for the prefix array. Mention that this is optimal for comparison-based sorting.

Key Points to Mention

  • Sorting dishes by difficulty and using binary search for each chef.
  • Prefix maximum array to avoid scanning all dishes for each chef.
  • Greedy choice: each chef independently picks the highest-profit dish they can cook.
  • Handling chefs with skill lower than all dish difficulties (profit 0).
  • Time and space complexity analysis.
  • Edge cases: empty arrays, all chefs unable to cook, multiple chefs same dish.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.