Product of Array Except Self

Description

Given an array nums of n integers where n > 1,  return an array output such that output[i] is equal to the product of all the elements of nums except nums[i].

Example:

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

Constraint: It's guaranteed that the product of the elements of any prefix or suffix of the array (including the whole array) fits in a 32 bit integer.

Note: Please solve it without division and in O(n).

Follow up:
Could you solve it with constant space complexity? (The output array does not count as extra space for the purpose of space complexity analysis.)

Solution(javascript)

// O(n) time O(1) space 有点类似 Prefix Sum 的思路
// const productExceptSelf = (nums = []) => {
//   const result = new Array(nums.length).fill(1)
//   let prev = 1
//   for (let i = 1; i < nums.length; i++) {
//     prev *= nums[i - 1]
//     result[i] = prev
//   }
//   prev = 1
//   for (let j = nums.length - 2; j >= 0; j--) {
//     prev *= nums[j + 1]
//     result[j] *= prev
//   }
//   return result
// }
const productExceptSelf = (nums = []) => {
    if(!nums.length) {
        return nums
    }
    const product = [nums[0]]
    for(let i = 1; i < nums.length; i++) {
        product[i] = nums[i] * product[i-1]
    }
    let suffixProduct = 1
    for(let i = nums.length -1; i >= 1; i--) {
        product[i] = product[i-1] * suffixProduct
        suffixProduct *= nums[i]
    }
    product[0] = suffixProduct
    return product
}