Cheapest flight within K stops

class Solution:
    def findCheapestPrice(self, n: int, flights: List[List[int]], src: int, dst: int, k: int) -> int:

        graph = defaultdict(list)
        for source, destination, price in flights:
            graph[source].append((destination, price))


        # pruning strategy
        # track min paths to reach a particular stop
        # avoid travelling down that path if the min
        # is already achieved
        stops = [float("inf")]*n

        # PQ: (cost, current_city, num_stops)
        pq = [(0, src, 0)]

        while pq:
            cost, current_city, num_stops = heapq.heappop(pq)

            # prune conditions
            # we have already found a path to this city with fewer stops
            # or max_total_flights (k+1) exceeded
            if num_stops >= stops[current_city] or num_stops > k + 1:
                continue

            # set min here
            stops[current_city] = num_stops

            # end condition
            if current_city == dst:
                return cost

            for nbr, price in graph[current_city]:
                heapq.heappush(pq, (cost + price, nbr, num_stops + 1))

        return -1