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[LeetCode 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.

Example 1

Input: nums = [1,2,3,4]
Output: [24,12,8,6]

Example 2

Input: nums = [-1,1,0,-3,3]
Output: [0,0,9,0,0]

Constraints

  • 2 <= nums.length <= 10^5
  • -30 <= nums[i] <= 30
  • The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer.

Follow up

Can you solve the problem in O(1) extra space complexity? (The output array does not count as extra space for space complexity analysis.)

Thoughts

  • We store preSum & postSum in result array

TypeScript

function productExceptSelf(nums: number[]): number[] {
  const res: number[] = []

  let prefix: number = 1
  for (let i = 0; i < nums.length; i++) {
    if (i === 0) {
      res[i] = 1
    } else {
      prefix *= nums[i - 1]
      res[i] = prefix
    }
  }

  let postfix: number = 1
  for (let i = nums.length - 2; i >= 0; i--) {
    postfix *= nums[i + 1]
    res[i] *= postfix
  }

  return res
}

Reference