MEDIUM NC#6 Blind #4 Arrays & Hashing
238. Product of Array Except Self
📖 Problem
Given an integer array nums, return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i]. The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer. You must write an algorithm that runs in O(n) time and without using the division operation.
🧠 Visual Learning Aid
1 Model the input into the right structure
2 Choose the core technique and invariant
3 Execute step-by-step with a sample
4 Validate complexity and edge cases
JS/TS Refreshers
- •Array methods (`push`, `pop`, `shift`, `slice`)
- •Object/Map/Set usage patterns
- •Function parameter and return typing
Logical Thinking Concepts
- •Define invariants before coding
- •Check edge cases first (`[]`, single element, duplicates)
- •Estimate time/space before implementation
💡 Approach
- → Compute prefix products from left to right
- → Compute suffix products from right to left
- → Result[i] = prefix[i] * suffix[i]
- → Can do in two passes without extra space for prefix/suffix arrays
- → Time: O(n), Space: O(1) excluding result array
🧭 Prerequisites
🛠️ Hints & Pitfalls
Hints
- •Compute prefix products from left to right
- •Compute suffix products from right to left
- •Result[i] = prefix[i] * suffix[i]
Common Pitfalls
- •Can do in two passes without extra space for prefix/suffix arrays
- •Time: O(n), Space: O(1) excluding result array
🧪 Test Cases
Hidden tests on submit: 1
Test Case 1
Not run Input:
productExceptSelf([1,2,3,4]); Expected:
[24, 12, 8, 6] Test Case 2
Not run Input:
productExceptSelf([-1,1,0,-3,3]); Expected:
[0, 0, 9, 0, 0] Test Case 3
Not run Input:
productExceptSelf([1,0]); Expected:
[0, 1] 📝 Code Editor
📤 Output