Minimum Rounds to Complete All Tasks LeetCode solution in C++

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class Solution {
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 public:
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  int minimumRounds(vector<int> &tasks) {
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    unordered_map<int, int> mp;
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    for (int i = 0; i < tasks.size(); i++) {
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      mp[tasks[i]]++;
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    }
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    int output = 0;
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    for (auto freq : mp) {
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      if (freq.second == 1) return -1;
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      if (freq.second % 3 == 0) {
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        output += freq.second / 3;
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      } else {
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        output += freq.second / 3 + 1;
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      }
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    }
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    return output;
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  }
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};