Daily Temperatures
Given an array of temperatures, return an array such that `answer[i]` is the number of days you have to wait after day $i$ to get a warmer temperature. Use a Monotonic Stack.
Why Interviewers Ask This
Airbnb asks this to evaluate your mastery of stack-based optimizations for time-sensitive problems. They specifically test if you can identify the O(n^2) brute-force trap and pivot to a Monotonic Stack solution, demonstrating your ability to optimize algorithms for real-world scalability where data volume is high.
How to Answer This Question
1. Clarify requirements: Confirm input constraints like array length and temperature ranges to determine edge cases.
2. Analyze complexity: Explicitly state that a nested loop approach yields O(n^2), which is inefficient for large datasets Airbnb handles daily.
3. Propose the pattern: Introduce the Monotonic Decreasing Stack concept as the optimal strategy to track indices of pending warmer days.
4. Walk through logic: Explain iterating backward or forward while popping elements smaller than current temperatures to find the nearest greater value.
5. Implement with comments: Write clean code focusing on index management and boundary checks, verbalizing each step to show your thought process clearly.
Key Points to Cover
- Identifying the O(n^2) brute force limitation immediately
- Correctly implementing a Monotonic Decreasing Stack
- Explaining the logic of popping indices based on temperature comparison
- Handling edge cases where no warmer day exists
- Achieving optimal O(n) time and space complexity
Sample Answer
I would start by acknowledging that a naive solution using nested loops results in O(n^2) time complexity, which isn't ideal for processing large streams of weather data efficiently. Instead, I propose using a Monotonic…
Common Mistakes to Avoid
- Using nested loops resulting in Time Limit Exceeded errors on large inputs
- Confusing the stack with storing values instead of indices, losing date context
- Forgetting to initialize the answer array with zeros for unprocessed days
- Incorrectly calculating the distance between current index and stack top
Sound confident on this question in 5 minutes
Answer once and get a 30-second AI critique of your structure, content, and delivery. First attempt is free — no signup needed.