Task Scheduler

Given a char array representing tasks CPU need to do. It contains capital letters A to Z. Each capital letter represents a different task. Tasks could be done without original order. Each task could be done in one interval. For each interval, CPU could complete one task or be idle. However, there is a constraint that at any moment, two same tasks should have at least n intervals. You need to return the least number of intervals the CPU will take to finish all the tasks.

int leastInterval(vector<char>& tasks, int n) {
  unordered_map<char, int> map;
  for (char task : tasks) {
    map[task]++;
  }
  int maxCount = 0, maxCountTask = 0;
  for (auto& pair : map) {
    if (pair.second > maxCount) {
      maxCount = pair.second;
      maxCountTask = 1;
    }
    else if (pair.second == maxCount) {
      maxCountTask++;
    }
  }
  return max((int)tasks.size(), (maxCount - 1) * (n + 1) + maxCountTask);
}