Network Delay Time

def networkDelayTime(times, n, k):
    edges = collections.defaultdict(list)
    for u, v, w in times:
        edges[u].append((v, w))
        
    minHeap = [(0, k)]
    visit = set()
    t = 0
    
    while minHeap:
        w1, n1 = heapq.heappop(minHeap)
        if n1 in visit:
            continue
        visit.add(n1)
        t = max(t, w1)
        
        for n2, w2 in edges[n1]:
            if n2 not in visit:
                heapq.heappush(minHeap, (w1 + w2, n2))
                
    return t if len(visit) == n else -1