0238-product-of-array-except-self.js

/**
 * 238. Product of Array Except Self
 * https://leetcode.com/problems/product-of-array-except-self/
 * Difficulty: Medium
 *
 * 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.
 */

/**
 * @param {number[]} nums
 * @return {number[]}
 */
var productExceptSelf = function(nums) {
  const emptyResult = new Array(nums.length).fill(0);
  const zeroCount = nums.filter(n => n === 0).length;
  if (zeroCount > 1) {
    return emptyResult;
  }
  const product = nums.reduce((product, n) => product * (n === 0 ? 1 : n), 1);
  if (zeroCount === 1) {
    emptyResult[nums.indexOf(0)] = product;
    return emptyResult;
  }
  return nums.map(n => product / n);
};

// https://leetcode.com/discuss/study-guide/5119937/prefix-sum-problems

// Brute Force
// var productExceptSelf = function (nums) {
//   const n = nums.length;
//   const res = new Array(n);

//   for (let i = 0; i < n; i++) {
//     let prod = 1;
//     for (let j = 0; j < n; j++) {
//       if (i !== j) {
//         prod *= nums[j];
//       }
//     }
//     res[i] = prod;
//   }
//   return res;
// };

// https://neetcode.io/problems/products-of-array-discluding-self
// https://www.youtube.com/watch?v=yuws7YK0Yng

// 2. Division
// 3. Prefix & Suffix
// 4. Prefix & Suffix (Optimal)