AI solution for JavaScript Coding Question on BFE.dev
167. Intersection of unsorted arrays

One possible solution is to use a hash table to count the occurrences of each item in the first array, then iterate over the second array and check if each item is in the hash table, and if so, add it to the result array and decrement its count in the hash table. This guarantees that we only output one occurrence of each common item, and runs in O(n) time and O(n) space, where n is the total number of items in both arrays. Here's the code:

function intersection(a, b) {
  const counts = {};
  const result = [];

  for (const x of a) {
    counts[x] = (counts[x] || 0) + 1;
  }

  for (const x of b) {
    if (counts[x]) {
      result.push(x);
      counts[x]--;
    }
  }

  return result;
}

Note that if the arrays are very large, we may need to use a more memory-efficient data structure for the hash table, such as a Map or a Bloom filter.