2336. Smallest Number in Infinite Set - LeetCode

import heapq


class SmallestInfiniteSet:
    def __init__(self):
        self.i = 0
        self.q = []

    def popSmallest(self) -> int:
        if self.q:
            return heapq.heappop(self.q)
        self.i += 1
        return self.i

    def addBack(self, num: int) -> None:
        if num <= self.i and num not in self.q:
            heapq.heappush(self.q, num)