50. 2336. Smallest Number in Infinite Set

Approach -1
class SmallestInfiniteSet {
    PriorityQueue<Integer> pq;
    HashSet<Integer> hs;

    public SmallestInfiniteSet() {
        pq = new PriorityQueue<>(1000);
        hs = new HashSet<>(1000);
        for(int i=0;i<1000;i++){
            pq.add(i+1);
            hs.add(i+1);
        }
        
    }
    
    public int popSmallest() {
        int num = pq.poll();
        hs.remove(num);
        return num;
        
    }
    
    public void addBack(int num) {
        if(!hs.contains(num)){
            hs.add(num);
            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);
 */

Approach - II
class SmallestInfiniteSet {
    int arr[];
    int i=1;
    public SmallestInfiniteSet() {
        arr=new int[1001];
    }
    
    public int popSmallest() {
        int j;
        for(j=i;i<1001;j++)
        if(arr[j]==0){
            arr[j]=1;
            i=j;
            break;
        }
        return j;
    }
    
    public void addBack(int num) {
        if(num<i)
        i=num;
        arr[num]=0;
    }
}

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