1792. Maximum Average Pass Ratio

class Solution {
public:
    double maxAverageRatio(vector<vector<int>>& classes, int extraStudents) {
        int classesLen = classes.size();
        
        // pq to know which class will increase the avg the most
        priority_queue<pair<double, int>> valueQueue;
        double finalAvg = 0;
        double localAvg = 0;


        // going through all classes adding them to finalAvg and
        // placing their avg increase into the pq if we were to add
        // an extra student there
        for (int i = 0; i < classesLen; ++i) {
            localAvg = static_cast<double>(classes[i][0]) / classes[i][1];
            valueQueue.push({(static_cast<double>(classes[i][0] + 1) / (classes[i][1] + 1)) - localAvg, i});
            finalAvg += localAvg;
        }

        // devide the avg once after the loop
        finalAvg /= classesLen;


        // while there are students to distribute we go through the pq
        while (extraStudents > 0) {
            // we take the class with highest avg inc value
            auto top = valueQueue.top();
            valueQueue.pop();

            // add the value / classLen to the finalAvg
            finalAvg += top.first / classesLen;

            // we add a student to that class
            ++classes[top.second][1];
            ++classes[top.second][0];

            // recalculate that class avg inc if we were to add an
            // extra student
            localAvg = static_cast<double>(classes[top.second][0]) / classes[top.second][1];
            valueQueue.push({(static_cast<double>(classes[top.second][0] + 1) / (classes[top.second][1] + 1)) - localAvg, top.second});
            
            // decrement the extraStudents left
            --extraStudents;
        }

        return finalAvg;
    }
};