How would you solve the Two Sum problem efficiently?
This classic interview question requires finding two numbers in an array that add up to a target value. It highlights the trade-off between brute force and hash map solutions.
Why Interviewers Ask This
This question is a staple because it effectively differentiates candidates who know basic iteration from those who understand hash-based lookups. Interviewers evaluate your ability to optimize space-time trade-offs. It also tests logical reasoning when dealing with duplicate values and index management.
How to Answer This Question
First, describe the brute-force O(n^2) approach to show baseline understanding. Then, pivot to the optimal O(n) solution using a hash map to store complements. Explain how you calculate the complement for each element and check its existence in the map. Ensure you mention how to handle indices correctly and avoid reusing the same element.
Key Points to Cover
- Brute force vs hash map
- Calculate complement dynamically
- Store indices in map
- O(n) time complexity
Sample Answer
I would start with a brute-force approach checking all pairs, which takes O(n^2) time. However, a more efficient solution uses a hash map to store elements as we iterate. For each number, I calculate the complement (targ…
Common Mistakes to Avoid
- Reusing the same element twice
- Ignoring unsorted input requirements
- Failing to return correct indices
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