Finding Pairs With a Certain Sum LeetCode solution in C++

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class FindSumPairs {
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 public:
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  unordered_map<int, int> mp2;
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  unordered_map<int, int> mp1;
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  vector<int> arr;
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  FindSumPairs(vector<int> &nums1, vector<int> &nums2) {
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    for (auto x : nums1) {
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      mp1[x]++;
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    }
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    arr = nums2;
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    for (auto x : nums2) {
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      mp2[x]++;
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    }
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  }
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  void add(int index, int val) {
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    mp2[arr[index]]--;
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    if (mp2[arr[index]] == 0) {
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      mp2.erase(arr[index]);
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    }
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    arr[index] += val;
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    mp2[arr[index]]++;
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  }
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  int count(int tot) {
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    int count = 0;
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    for (auto x : mp1) {
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      int val = x.first;
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      int freq = x.second;
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      int need = tot - val;
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      if (mp2.count(need)) {
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        count += mp2[need] * freq;
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      }
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    }
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    return count;
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  }
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};
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/**
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 * Your FindSumPairs object will be instantiated and called as such:
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 * FindSumPairs* obj = new FindSumPairs(nums1, nums2);
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 * obj->add(index,val);
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 * int param_2 = obj->count(tot);
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 */