leetcode/work/Medium/Array/238.product-of-array-except-self.js

/*
 * 238. Product of Array Except Self
 * Difficulty: Medium
 * https://leetcode.com/problems/product-of-array-except-self/
 * 
 * ──────────────────────────────────────────────────
 * 
 * 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 input is generated such that answer[i] 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.)
*/

/**
 * @param {number[]} nums
 * @return {number[]}
 */
var productExceptSelf = function(nums) {
  const n = nums.length;
  const answer = new Array(n).fill(1);
  const rightArr = new Array(n).fill(1);

  for (let i = 1; i < n; i++) {
    answer[i] = nums[i - 1] * answer[i - 1];
  }
  for (let i = n - 2; i >= 0; i--) {
    rightArr[i] = nums[i + 1] * rightArr[i + 1];
  }
  for (let i = 0; i < n; i++) {
    answer[i] *= rightArr[i];
  }
  return answer;
};