0350. Intersection of Two Arrays II.js

// Given two arrays, write a function to compute their intersection.
//
// Example:
// Given nums1 = [1, 2, 2, 1], nums2 = [2, 2], return [2, 2].
//
// Note:
//   Each element in the result should appear as many times as it shows in both arrays.
//   The result can be in any order.
//
// Follow up:
//   What if the given array is already sorted? How would you optimize your algorithm?
//   What if nums1's size is small compared to nums2's size? Which algorithm is better?
//   What if elements of nums2 are stored on disk, and the memory is limited such that you cannot load all elements into the memory at once?

/**
 * @param {number[]} nums1
 * @param {number[]} nums2
 * @return {number[]}
 */

const intersect = (nums1, nums2) => {
  let res = [];
  const map = {};

  for (const n of nums1) {
    if (map[n] == null) map[n] = 0;
    map[n]++;
  }

  for (const n of nums2) {
    if (map[n] > 0) {
      res.push(n);
      map[n]--;
    }
  }
  return res;
};