[Interview type questions] Task sequence arragnement

Given a task sequence and the cool down time(k), rearrange the task sequence such that the execution time is minimal.

Solution:

 public static void main(String[] args) {
  char[] task = findBestTaskArrangement(String.valueOf("AAABBB").toCharArray(), 2);
  System.out.println(task);
  System.out.println("Total time: " + computeTatalTaskTime(task, 2));
  // ABABAB
  // Total time:8
 }
 
 public static char[] findBestTaskArrangement(char[] tasks, int k) {
  int n = tasks.length;
  Map<Character, Integer> map = new HashMap<>();
  for (char task : tasks) {
   map.put(task, map.getOrDefault(task, 0) + 1);
  }

  PriorityQueue<Task> queue = new PriorityQueue<>(new Comparator<Task>() {

   @Override
   public int compare(Task a, Task b) {
    return b.frequency - a.frequency;
   }
  });

  for (Map.Entry<Character, Integer> entry : map.entrySet()) {
   queue.offer(new Task(entry.getKey(), entry.getValue()));
  }
  
  tasks = new char[n];
  int i = 0;
  while (!queue.isEmpty()) {
   int c = 0;
   List<Task> nextRoundTask = new ArrayList<>();
   while(c++ < k && !queue.isEmpty()) {
    Task task = queue.poll();
    task.frequency--;
    // Locate the next empty slot
    tasks[i++] = task.id;
    if (task.frequency > 0)
     nextRoundTask.add(task);
   }
   for (Task task : nextRoundTask) {
    queue.offer(task);
   }
  }

  return tasks;
 }

 // helper class
 public static class Task {
  char id;
  int frequency;

  Task(char i, int f) {
   id = i;
   frequency = f;
  }
 }

 public static int computeTatalTaskTime(char[] tasks, int k) {
  HashMap<Character, Integer> taskLastTimeMap = new HashMap<>();
  int currTime = 0;
  for (char task : tasks) {
   if (taskLastTimeMap.containsKey(task)) {
    int exceptedTime = taskLastTimeMap.get(task) + k + 1;
    if (exceptedTime > currTime) {
     currTime = exceptedTime;
    } else
     currTime++;
   } else {
    currTime++;
   }
   taskLastTimeMap.put(task, currTime);
  }
  return currTime;
 }