350. Intersection of Two Arrays II

 JAVA

• class Solution {
      public int[] intersect(int[] nums1, int[] nums2) {
          Map<Integer, Integer> counter = new HashMap<>();
          for (int num : nums1) {
              counter.put(num, counter.getOrDefault(num, 0) + 1);
          }
          List<Integer> t = new ArrayList<>();
          for (int num : nums2) {
              if (counter.getOrDefault(num, 0) > 0) {
                  t.add(num);
                  counter.put(num, counter.get(num) - 1);
              }
          }
          int[] res = new int[t.size()];
          for (int i = 0; i < res.length; ++i) {
              res[i] = t.get(i);
          }
          return res;
      }
  }

C++

• class Solution {
  public:
      vector<int> intersect(vector<int>& nums1, vector<int>& nums2) {
          unordered_map<int, int> counter;
          for (int num : nums1) ++counter[num];
          vector<int> res;
          for (int num : nums2) {
              if (counter[num] > 0) {
                  --counter[num];
                  res.push_back(num);
              }
          }
          return res;
      }
  };