Maximum Length of Subarray With Positive Product

MediumDynamic Programming1d dp

Solve this the way you would in the interview: out loud, on a timer, with an AI interviewer asking follow-ups while you code. You get a scored report at the end.

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Problem

Given an integer array nums, find the longest contiguous subarray whose product of all elements is strictly **positive**. Return its length, or 0 if no such subarray exists. Do not actually multiply the values; products overflow quickly. Aim for O(n) time and O(1) extra space.

Examples

Input: nums = [1,-2,-3,4]
Output: 4
The two negatives cancel, so the whole array has a positive product (24).
Input: nums = [0,1,-2,-3,-4]
Output: 3
The best is [1,-2,-3]; including -4 would make the product negative, and 0 cannot be included.
Input: nums = [-1,-2,-3,0,1]
Output: 2
[-1,-2] and [-2,-3] both have positive products of length 2.

Constraints

  • 1 <= nums.length <= 10^5
  • -10^9 <= nums[i] <= 10^9

What the interviewer grades

A correct solution is one of five scores. The report also grades problem understanding (did you clarify inputs and edge cases before coding), problem solving, communication while you work, code quality, and testing. See a sample report, or read up on the pattern in the lessons.

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