238__medium__product-of-array-except-self.js

/**

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]
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.)

 */

/**
 *
 * O(n) time
 * O(n) space
 *
 */
var productExceptSelf = function(nums) {
  if (!nums || nums.length === 0) return nums;

  let res = new Array(nums.length).fill(1);

  for (let i = 1; i < nums.length; i++) {
      res[i] = res[i-1] * nums[i-1];
  }

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

  return res;
};