[LC] 350. Intersection of Two Arrays II

class Solution {
    public int[] intersect(int[] nums1, int[] nums2) {
        if (nums1 == null || nums2 == null) {
            return null;
        }
        Map<Integer, Integer> map = new HashMap<>();
        List<Integer> list = new ArrayList<>();
        for (int num: nums1) {
            map.put(num, map.getOrDefault(num, 0) + 1);
        }
        for (int num: nums2) {
            if (map.containsKey(num) && map.get(num) > 0) {
                list.add(num);
                map.put(num, map.get(num) - 1);
            }
        }
        int[] res = new int[list.size()];
        for (int k = 0; k < res.length; k++) {
            res[k] = list.get(k);
        }
        return res;
    }
}