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class Solution {
public:
    int leastInterval(vector<char>& tasks, int n) {
        unordered_map<char, int> freq;
        for (const char& c : tasks) {
            ++ freq[c];
        }

        int m = freq.size();
        vector<int> nextValid, rest;
        for (auto [_, v]: freq) {
            nextValid.push_back(1);
            rest.push_back(v);
        }

        int time = 0;
        for (int i = 0; i < tasks.size(); ++ i) {
            ++ time;
            int minNextValid = INT_MAX;
            for (int j = 0; j < m; j ++) {
                if (rest[j]) {
                    minNextValid = min(minNextValid, nextValid[j]);
                }
            }
            time = max(time, minNextValid);
            int best = -1;
            for (int j = 0; j < m; j ++) {
                if (rest[j]  && nextValid[j] <= time) {
                    if (best == -1 | rest[j] > rest[best]) {
                        best = j;
                    }
                }
            }
            nextValid[best] = time + n + 1;
            -- rest[best];
        }

        return time;
    }
};