Product of Array Except Self

Product of Array Except Self - LeetCodeLeetCode

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]

Pseudocode

- don't understand how this solution was derived

- to study more 
https://leetcode.com/problems/product-of-array-except-self/solutions/1597994/c-python-4-simple-solutions-w-explanation-prefix-suffix-product-o-1-space-approach/

Solution

// from solutions page mindblown
const productExceptSelf = function (nums) {
  let output = [];
  let leftMult = 1;
  let rightMult = 1;

  // reassigns previous product multiplication, doesn't include itself
  for (let i = nums.length - 1; i >= 0; i--) {
    output[i] = rightMult;
    rightMult *= nums[i];
    // console.log(output[i], rightMult, nums[i])
  }

  // left side multiplication required to circle back
  for (let j = 0; j < nums.length; j++) {
    output[j] *= leftMult;
    leftMult *= nums[j];
    // console.log(output[j], leftMult, nums[j])
  }
  return output;
};

Time and Space Complexity

Time

• What did the code do

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Space

• What did the code do

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