238 Product of Array Except Self 1

Joel Castillo Espinosa 2

DESCRIPTION

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.

Examples

  • 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

SOLUTION 3

prod_array <- function(nums){
  # reverse of the vector 
  nums_rev <- rev(nums)
  leng_nums <- length(nums)
  
  # calculate for each i:
    # for the i element the product is defined by product 
    # of elements 1 to i-1 (left_p) and the product of the 
    # elements i+1 to the last (right_p)
  left_p <- c(1,cumprod(nums[-leng_nums]))
  right_p <-c(1,cumprod(nums_rev[-leng_nums]))
  
  
  result <- left_p * rev(right_p)
  return(result)
}

Examples using the function

We can use the examples presented before.

prod_array(c(1,2,3,4))

## [1] 24 12  8  6

prod_array(nums = c(-1,1,0,-3,3))

## [1] 0 0 9 0 0

  1. This problem is originally from LeetCode, you can find it in Leetcode. ↩

  2. Email: jocastillo@colmex.mx. For more content visit my website: https://joelcastillo.netlify.app
    If you have any questions or suggestions, I’d be grateful to hear from you. ↩

  3. This solution is entirely my own work. It was developed using R version 4.4.1 (2024-06-14 ucrt). ↩