最短路径

import heapq

graph = {0: [(1, 2), (2, 5)], 1: [(2, 1), (3, 3)], 2: [(3, 2)], 3: []}

def dijkstra(start):
    dist = {start: 0}
    pq = [(0, start)]
    while pq:
        d, u = heapq.heappop(pq)
        if d != dist[u]:
            continue
        for v, w in graph[u]:
            nd = d + w
            if nd < dist.get(v, 1e18):
                dist[v] = nd
                heapq.heappush(pq, (nd, v))
    return dist

print(dijkstra(0))