621_Task_Scheduler

Leetcode 621: Task Scheduler
Detailed video explanation: https://youtu.be/tGw5GbDekTU
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C++:
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class Solution {
public:
    int leastInterval(vector<char>& tasks, int n) {
        unordered_map<char, int> counts;
        for(char t: tasks) 
            counts[t]++;
        priority_queue<int> pq;
        for(auto c: counts)
            pq.push(c.second);
        
        int result = 0;
        while(!pq.empty()){
            int time = 0;
            vector<int> tmp;
            for(int i = 0; i < n+1; ++i){
                if(!pq.empty()){
                    tmp.push_back(pq.top() - 1);
                    pq.pop();
                    time++;
                }
            }
            for(auto t: tmp)
                if(t) pq.push(t);
            result += pq.empty() ? time : n+1;
        }
        return result;
    }
};


Java:
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class Solution {
    public int leastInterval(char[] tasks, int n) {
        Map<Character, Integer> counts = new HashMap();
        for(char t: tasks) 
            counts.put(t, counts.getOrDefault(t, 0) + 1);
        PriorityQueue<Integer> pq = new PriorityQueue(counts.size(), Collections.reverseOrder());
        pq.addAll(counts.values());
        
        int result = 0;
        while(!pq.isEmpty()){
            int time = 0;
            List<Integer> tmp = new ArrayList();
            for(int i = 0; i < n+1; ++i){
                if(!pq.isEmpty()){
                    tmp.add(pq.remove() - 1);
                    time++;
                }
            }
            for(int t: tmp)
                if(t > 0) pq.add(t);
            result += pq.isEmpty() ? time : n+1;
        }
        return result;
    }
}