2244

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:

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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Solution 1.

// OJ: https://leetcode.com/problems/minimum-rounds-to-complete-all-tasks/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(U) where `U` is the count of distinct numbers in `A`.
class Solution {
public:
    int minimumRounds(vector<int>& A) {
        unordered_map<int, int> m;
        for (int n : A) m[n]++;
        int ans = 0;
        for (auto &[n, cnt] : m) {
            if (cnt % 3 == 0) ans += cnt / 3;
            else if (cnt % 3 == 1) {
                if (cnt == 1) return -1;
                ans += 2 + (cnt - 4) / 3;
            } else ans += 1 + (cnt - 1) / 3;
        }
        return ans;
    }
};

Or

// OJ: https://leetcode.com/problems/minimum-rounds-to-complete-all-tasks/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(U) where `U` is the count of distinct numbers in `A`.
class Solution {
public:
    int minimumRounds(vector<int>& A) {
        unordered_map<int, int> m;
        for (int n : A) m[n]++;
        int ans = 0;
        for (auto &[n, cnt] : m) {
            if (cnt == 1) return -1;
            ans += (cnt + 2) / 3;
        }
        return ans;
    }
};