What is the optimal approach to find a subarray with a given sum?
Candidates must find a contiguous subarray whose elements sum up to a specific target value. This tests sliding window techniques and hash map usage.
Why Interviewers Ask This
This classic problem evaluates knowledge of the sliding window technique and prefix sum concepts. Interviewers want to see if you can solve it in linear time O(n). It also tests handling of negative numbers and non-negative constraints.
How to Answer This Question
Discuss two approaches: one for non-negative numbers using a sliding window, and another for general numbers using a hash map to store prefix sums. Explain how the sliding window expands and contracts based on the current sum. For the hash map approach, explain how looking for (current_sum - target) finds the subarray.
Key Points to Cover
- Use sliding window for non-negative arrays
- Apply hash map for arrays with negative numbers
- Maintain running sum and check for target difference
- Ensure O(n) time complexity
Sample Answer
If the array contains only non-negative numbers, I would use a sliding window. I expand the right pointer until the sum equals or exceeds the target. If it exceeds, I shrink from the left until the sum is valid again. If…
Common Mistakes to Avoid
- Attempting to use brute force O(n^2) solutions
- Failing to handle negative numbers correctly with sliding window
- Not resetting the window start index properly
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.