How can you compute the product of all array elements except self?
This problem requires creating an output array where each element is the product of all other elements in the input array. It tests division avoidance and prefix/suffix product techniques.
Why Interviewers Ask This
Interviewers use this to assess a candidate's ability to think outside the box regarding division operations, especially when zero is involved. They want to see if you can construct prefix and suffix products to solve the problem without using division. This demonstrates advanced array manipulation skills and attention to edge cases.
How to Answer This Question
Explain why division might fail due to zeros and propose an alternative. Describe the prefix product approach where you calculate the product of all elements to the left of each index. Then, describe the suffix product approach for elements to the right. Combine these in a second pass to generate the final result. Emphasize achieving O(n) time and O(1) extra space (excluding output).
Key Points to Cover
- Avoiding division for zero handling
- Prefix product calculation
- Suffix product calculation
- In-place modification for O(1) space
Sample Answer
Instead of using division which fails with zeros, I would use prefix and suffix products. First, I create an output array initialized to ones. In the first pass, I fill the output array with the product of all elements t…
Common Mistakes to Avoid
- Attempting to use division blindly
- Creating separate arrays for left and right products instead of reusing output
- Incorrectly initializing the output array
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