package q2336

import "container/heap"

type MinHeap []int

func (m *MinHeap) Len() int               { return len(*m) }
func (m *MinHeap) Less(i int, j int) bool { return (*m)[i] < (*m)[j] }
func (m *MinHeap) Push(x any)             { *m = append(*m, x.(int)) }
func (m *MinHeap) Swap(i int, j int)      { (*m)[i], (*m)[j] = (*m)[j], (*m)[i] }

func (m *MinHeap) Pop() any {
	ret := (*m)[len(*m)-1]
	*m = (*m)[:len(*m)-1]
	return ret
}

type SmallestInfiniteSet struct {
	head  int
	added MinHeap
}

func Constructor() SmallestInfiniteSet {
	return SmallestInfiniteSet{
		head:  1,
		added: MinHeap{},
	}
}

func (s *SmallestInfiniteSet) PopSmallest() int {
	if s.added.Len() > 0 {
		top := s.added[0]
		for s.added.Len() > 0 && s.added[0] == top {
			heap.Pop(&s.added)
		}
		return top
	} else {
		s.head++
		return s.head - 1
	}
}

func (s *SmallestInfiniteSet) AddBack(num int) {
	if num >= s.head {
		return
	}
	heap.Push(&s.added, num)
}

/**
 * Your SmallestInfiniteSet object will be instantiated and called as such:
 * obj := Constructor();
 * param_1 := obj.PopSmallest();
 * obj.AddBack(num);
 */