1834. Single-Threaded CPU

class Solution {
    public int[] getOrder(int[][] tasks) {
        //How to store the tasks
        //Task(index, startTime, processingTime)
        //Sort : StartTime ==> processingTime

        int n = tasks.length;
        Task[] t = new Task[n];
        for(int i = 0; i < n; i++) {
            t[i] = new Task(i, tasks[i][0], tasks[i][1]);
        }

        Arrays.sort(t, (a,b) -> a.startTime == b.startTime ? a.processingTime- b.processingTime : a.startTime - b.startTime);


        //How to pick the task
        //Priority Queue
        //Sorting => ProcessingTime (asc) ==> index (asc)

        PriorityQueue<Task> waitingTasks = new PriorityQueue<>((a,b) -> a.processingTime == b.processingTime ? a.index-b.index : a.processingTime - b.processingTime);

        int[] result = new int[n];
        int index = 0, resIndex = 0;
        int endTime = 0;

        while(index < n) {
            if(waitingTasks.size() > 0) {
                //Calculate new EndTime and process one task
                //Pick the next Task, calculte the new endTime, Fill the waitingTasks Queue
                Task currentTask = waitingTasks.remove();
                endTime = Math.max(currentTask.startTime, endTime) + currentTask.processingTime;
                result[resIndex++] = currentTask.index;

                while(index < n && endTime >= t[index].startTime) {
                    waitingTasks.add(t[index++]);
                }
            }
            else {
                //Add a task in waitingTasks List
                waitingTasks.add(t[index++]);
            }
        }

        while(waitingTasks.size() > 0) {
            Task task = waitingTasks.remove();
            result[resIndex++] = task.index;
        }

        return result;
    }

    class Task {
        int index;
        int startTime;
        int processingTime;

        Task(int index, int startTime, int processingTime) {
            this.index = index;
            this.startTime= startTime;
            this.processingTime = processingTime;
        }
    }
}