# 2244. Minimum Rounds to Complete All Tasks

Medium
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:
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:
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`

### 解題

Runtime: 146 ms, faster than 100.00%
Memory Usage: 9.1 MB, less than 87.76%