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class Solution {
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 public:
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  vector<int> assignTasks(vector<int> &servers, vector<int> &tasks) {
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    priority_queue<vector<long long>, vector<vector<long long>>, greater<vector<long long>>> free,
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        busy;
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    for (int i = 0; i < servers.size(); ++i) {
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      free.push(vector<long long>{servers[i], i});
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    }
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    vector<int> ans;
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    long long time = 0;
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    queue<int> task_queue;
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    while (ans.size() < tasks.size()) {
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      // Bring all eligible tasks to task_queue.
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      for (int i = ans.size() + task_queue.size(); i <= time && i < tasks.size(); ++i) {
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        task_queue.push(tasks[i]);
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      }
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      // Bring all eligible servers to free queue.
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      while (!busy.empty() && busy.top()[0] <= time) {
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        auto &top = busy.top();
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        free.push(vector<long long>{top[1], top[2]});
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        busy.pop();
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      }
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      // If we have no servers, we cannot match until one of the servers becomes
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      // free.
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      if (free.empty()) {
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        time = busy.top()[0];
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        continue;
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      }
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      while (!task_queue.empty() && !free.empty()) {
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        // Now we just take the first task and first server as per defined
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        // priority and match the two.
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        int task = task_queue.front();
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        auto &top = free.top();
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        ans.push_back(top[1]);
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        busy.push(vector<long long>{time + task, top[0], top[1]});
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        task_queue.pop();
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        free.pop();
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      }
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      // Only increment time to receive new tasks once we have processed all
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      // tasks so far.
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      if (task_queue.empty()) time++;
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    }
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    return ans;
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  }
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};