Intersection of Two Arrays II

Problem

Given two integer arrays nums1 and nums2, return an array of their intersection. Each element in the result must appear as many times as it shows in both arrays and you may return the result in any order.

Example 1:

Input: nums1 = [1,2,2,1], nums2 = [2,2]
Output: [2,2]
Example 2:

Input: nums1 = [4,9,5], nums2 = [9,4,9,8,4]
Output: [4,9]
Explanation: [9,4] is also accepted.

Constraints:

  • 1 <= nums1.length, nums2.length <= 1000
  • 0 <= nums1[i], nums2[i] <= 1000

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?

Solution

Gross code.

class Solution {
    // space: o(n)
    // time: o(n)
    public int[] intersect(int[] nums1, int[] nums2) {
        var counts1 = new HashMap<Integer, Integer>();
        var counts2 = new HashMap<Integer, Integer>();
        for (var i : nums1) {
            counts1.compute(i, (key, value) -> (value == null) ? 1 : value + 1);
        }
        for (var i : nums2) {
            counts2.compute(i, (key, value) -> (value == null) ? 1 : value + 1);
        }

        var intersection = new ArrayList<Integer>();
        for (var entry : counts1.entrySet()) {
            var val1 = counts1.get(entry.getKey());
            var val2 = counts2.getOrDefault(entry.getKey(), 0);

            while (val1 != 0 && val2 != 0) {
                val1 -= 1;
                val2 -= 1;
                intersection.add(entry.getKey());
            }
        }

        // convert type
        var out = new int[intersection.size()];
        for (var i = 0; i < out.length; i++) {
            out[i] = intersection.get(i);
        }
        return out;
    }
}

Recent posts from blogs that I like

AI assisted search-based research actually works now

via Simon Willison

Changing Paintings: 67 Circe and her swine

Ulysses visits Circe's island, where his crew are turned into swine. When she tries to do the same with him, he refuses. They marry and spend a year together.

via The Eclectic Light Company

I'm on GitHub Sponsors

If you wanted to give me money but Patreon was causing grief, I'm on GitHub Sponsors now! Help me reach my goal of saving the world from AI scrapers with the power of anime.

via Xe Iaso