Task Scheduler
You are given an array of CPU tasks, each represented by letters A to Z, and a cooling time, n. Each cycle or interval allows the completion of one task. Tasks can be completed in any order, but there's a constraint: identical tasks must be separated by at least n intervals due to cooling time.
Return the minimum number of intervals required to complete all tasks.
public int leastInterval(char[] tasks, int n) {
Map<Character, Integer> map = new HashMap<>();
for (int i = 0; i < tasks.length; i++) {
map.put(tasks[i], map.getOrDefault(tasks[i], 0) + 1); // map key is TaskName, and value is number of times to be executed.
}
PriorityQueue<Map.Entry<Character, Integer>> q = new PriorityQueue<>( //frequency sort
(a,b) -> a.getValue() != b.getValue() ? b.getValue() - a.getValue() : a.getKey() - b.getKey());
q.addAll(map.entrySet());
int count = 0;
while (!q.isEmpty()) {
int k = n + 1;
List<Map.Entry> tempList = new ArrayList<>();
while (k > 0 && !q.isEmpty()) {
Map.Entry<Character, Integer> top = q.poll(); // most frequency task
top.setValue(top.getValue() - 1); // decrease frequency, meaning it got executed
tempList.add(top); // collect task to add back to queue
k--;
count++; //successfully executed task
}
for (Map.Entry<Character, Integer> e : tempList) {
if (e.getValue() > 0) q.add(e); // add valid tasks
}
if (q.isEmpty()) break;
count = count + k; // if k > 0, then it means we need to be idle
}
return count;
}
Posted by Jamie Meyer 19 days ago