Leetcode 2336

Consider we have a full infinite set at first Use a running curr to keep track of smallest number and priority queue to keep track if we have scarlet numbers before running smallest

class SmallestInfiniteSet {
    PriorityQueue<Integer> pq = new PriorityQueue<>();
    int curr;
    public SmallestInfiniteSet() {
        // set curr smallest to 1
        curr = 1;
    }
    
    public int popSmallest() {
        if(!pq.isEmpty())return pq.poll();
        // if we have nothing in pq, curr smallest is what we poll out, and sus next number would be curr + 1
        curr ++;
        return curr - 1;
    }
    
    public void addBack(int num) {
        if(num < curr & !pq.contains(num)){
            // number is small and we dont have it in our pq 
            // add back
            pq.add(num);
        }
    }
}

/**
 * Your SmallestInfiniteSet object will be instantiated and called as such:
 * SmallestInfiniteSet obj = new SmallestInfiniteSet();
 * int param_1 = obj.popSmallest();
 * obj.addBack(num);
 */