Find the Difference of Two Arrays LeetCode solution in C++

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// OJ:
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// https://leetcode.com/contest/weekly-contest-286/problems/find-the-difference-of-two-arrays/
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// Author: github.com/lzl124631x
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// Time: O(A + B)
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// Space: O(A + B)
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class Solution {
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 public:
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  vector<vector<int>> findDifference(vector<int> &A, vector<int> &B) {
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    unordered_set<int> sa(begin(A), end(A)), sb(begin(B), end(B));
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    vector<vector<int>> ans(2);
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    for (int n : sa) {
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      if (sb.count(n) == 0) ans[0].push_back(n);
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    }
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    for (int n : sb) {
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      if (sa.count(n) == 0) ans[1].push_back(n);
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    }
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    return ans;
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  }
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};