1834

class Solution {
public:
    typedef pair<int, int> pii;
    vector<int> getOrder(vector<vector<int>>& tasks) {
        priority_queue<pii, vector<pii>, greater<pii>> pq;
        long int time=0, N=tasks.size();
        vector<int> res;

        // Add index to tasks and sort the tasks based on enqueue time.
        for(int i=0; i<N; i++)
            tasks[i].push_back(i);
        sort(tasks.begin(), tasks.end());

        int i=0;
        while(!pq.empty() || i<N){
            // If heap is empty and cpu is idle, move time to start of next task.
            if(pq.empty())
                time = max(time, long(tasks[i][0]));

            // Add all tasks whose enqueue time is less than current time.
            while(i<N && tasks[i][0] <= time){
                pq.push({tasks[i][1], tasks[i][2]});
                i++;
            }

            // Pick up the least processing time task and execute.
            time += pq.top().first;
            res.push_back(pq.top().second);
            pq.pop();
        }
        return res;
    }
};