Product of Array Except Self
The key idea
The answer at index
i is the product of everything to its left times the product of everything to its right. Sweep left to fill prefix products, then sweep right multiplying in suffix products on the fly — so no division and no extra arrays.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.
Constraints
2 <= nums.length <= 10^5-30 <= nums[i] <= 30- The product of any prefix or suffix of
numsis guaranteed to fit in a 32-bit integer.
Examples
Input: nums = [1,2,3,4]
Output: [24,12,8,6]
Input: nums = [-1,1,0,-3,3]
Output: [0,0,9,0,0]
Complexity
Time: O(n) Space: O(1)
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