2244 Minimum Rounds to Complete All Tasks

You are given a 0-indexed integer array tasks, where tasks[i] represents the difficulty level of a task. In each round, you can complete either 2 or 3 tasks of the same difficulty level.

Return the minimum rounds required to complete all the tasks, or -1 if it is not possible to complete all the tasks.

Example 1:

Input: tasks = [2,2,3,3,2,4,4,4,4,4]
Output: 4
Explanation: To complete all the tasks, a possible plan is:
- In the first round, you complete 3 tasks of difficulty level 2. 
- In the second round, you complete 2 tasks of difficulty level 3. 
- In the third round, you complete 3 tasks of difficulty level 4. 
- In the fourth round, you complete 2 tasks of difficulty level 4.  
It can be shown that all the tasks cannot be completed in fewer than 4 rounds, so the answer is 4.

Example 2:

Input: tasks = [2,3,3]
Output: -1
Explanation: There is only 1 task of difficulty level 2, but in each round,
you can only complete either 2 or 3 tasks of the same difficulty level.
Hence, you cannot complete all the tasks, and the answer is -1.

Constraints:

• 1 <= tasks.length <= 105
• 1 <= tasks[i] <= 109

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class Solution:
    def minimumRounds(self, tasks: List[int]) -> int:
        count = defaultdict(int)
        for t in tasks:
            count[t] += 1
        
        res = 0
        for v in count.values():
            if v < 2:
                return -1
            res += v // 3
            if v % 3:
                res += 1
        return res

'''
Short version
'''
class Solution:
        def minimumRounds(self, tasks):
            freq = Counter(tasks).values()
            return -1 if 1 in freq else sum((a + 2) // 3 for a in freq)