Network Delay Time

import heapq
from collections import defaultdict

class Solution:
    def networkDelayTime(
        self, times: list[list[int]], n: int, k: int
    ) -> int:
        graph = defaultdict(list)
        for u, v, w in times:
            graph[u].append((v, w))
        dist = {}
        heap = [(0, k)]
        while heap:
            d, node = heapq.heappop(heap)
            if node in dist:
                continue
            dist[node] = d
            for neighbor, w in graph[node]:
                if neighbor not in dist:
                    heapq.heappush(heap, (d + w, neighbor))
        return max(dist.values()) if len(dist) == n else -1