Number of Orders in the Backlog LeetCode solution in C++

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class Solution {
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 public:
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  int getNumberOfBacklogOrders(vector<vector<int>> &orders) {
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    int n = orders.size();
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    // 0 - buy  , 1 - sell;
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    priority_queue<vector<int>> buyBacklog;
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    priority_queue<vector<int>, vector<vector<int>>, greater<vector<int>>> sellBacklog;
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    for (auto order : orders) {
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      if (order[2] == 0)
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        buyBacklog.push(order);
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      else
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        sellBacklog.push(order);
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      while (!buyBacklog.empty() && !sellBacklog.empty() &&
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             sellBacklog.top()[0] <= buyBacklog.top()[0]) {
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        auto btop = buyBacklog.top();
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        buyBacklog.pop();
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        auto stop = sellBacklog.top();
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        sellBacklog.pop();
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        int diff = btop[1] - stop[1];
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        if (diff > 0) {
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          btop[1] = diff;
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          buyBacklog.push(btop);
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        } else if (diff < 0) {
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          stop[1] = abs(diff);
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          sellBacklog.push(stop);
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        }
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      }
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    }
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    int ans = 0, mod = 1e9 + 7;
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    while (!buyBacklog.empty()) {
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      ans = (ans + buyBacklog.top()[1]) % mod;
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      buyBacklog.pop();
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    }
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    while (!sellBacklog.empty()) {
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      ans = (ans + sellBacklog.top()[1]) % mod;
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      sellBacklog.pop();
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    }
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    return ans;
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  }
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};