taskScheduler.java

public int leastInterval(char[] tasks, int n) {
        
    int task[] = new int[26];               // Task array to store the count of each task,
                                            // initialised to 0.
    
    for(char i : tasks)  // For-each loop to iterate over tasks and update the task 
        task[i - 'A']++; // frequencies simultaneously.
    
    Arrays.sort(task);          // Sorting the frequencies in ascending order so
                                // that the highest frequencies come to last. 
    
    int max_v = task[25] - 1; // Max value of frequency of tasks.
    int idle = max_v * n;     // Maximum number of idle slots we can have.
    
    for(int i = 24; i >= 0; i--){           // Iterating over frequencies, except the
                                            // maximum freq. we obtained earlier
        
        idle = idle - Math.min(max_v, task[i]); // Updating the idle slots because as we do
                                                // some more tasks, the slots would be
                                                // filled and no. of idle slots will reduce.
    }                                       
                                                        
    if(idle < 0)    // If all idle slots are filled or there are even more tasks than no.
        idle = 0;   // of idle slots, our answer would be no. of tasks in total i.e. 
                    // CPU would be busy the entire time, and cooldown time between all 
                    // tasks would be satisfied.
    
                                // Total cycles needed. If there are idle slots present
    return tasks.length + idle; // we add them to total tasks.
}