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349. Intersection of Two Arrays

  • Time: $O(n)$
  • Space: $O(n)$
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class Solution {
 public:
  vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
    vector<int> ans;
    unordered_set<int> set{nums1.begin(), nums1.end()};

    for (const int num : nums2)
      if (set.erase(num))
        ans.push_back(num);

    return ans;
  }
};

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class Solution {
  public int[] intersection(int[] nums1, int[] nums2) {
    List<Integer> ans = new ArrayList<>();
    Set<Integer> set = Arrays.stream(nums1).boxed().collect(Collectors.toSet());

    for (final int num : nums2)
      if (set.remove(num))
        ans.add(num);

    return ans.stream().mapToInt(Integer::intValue).toArray();
  }
}

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class Solution:
  def intersection(self, nums1: list[int], nums2: list[int]) -> list[int]:
    ans = []
    nums1 = set(nums1)

    for num in nums2:
      if num in nums1:
        ans.append(num)
        nums1.remove(num)

    return ans