By Long Luo

This article is the solution Java HashSet Solution of Problem 2215. Find the Difference of Two Arrays.

Intuition

We can use \(\texttt{HashSet}\) to record the distinct integers of the two arrays and judge whether a distinct integer in \(\textit{nums}_1\) which not present in \(\textit{nums}_2\).

We can only use \(2\) \(\texttt{HashSet}\), not \(4\) \(\texttt{HashSet}\).

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public List<List<Integer>> findDifference(int[] nums1, int[] nums2) {
    Set<Integer> set1 = new HashSet<>();
    Set<Integer> set2 = new HashSet<>();
    for (int num : nums1) {
        set1.add(num);
    }
    for (int num : nums2) {
        set2.add(num);
        set1.remove(num);
    }

    for (int num : nums1) {
        set2.remove(num);
    }

    List<List<Integer>> ans = new ArrayList<>();
    ans.add(new ArrayList<>(set1));
    ans.add(new ArrayList<>(set2));
    return ans;        
}

Analysis

• Time Complexity: \(O(m+n)\).
• Space Complexity: \(O(m+n)\).

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