Bellman_ford 队列优化算法（又名SPFA）

'''
def main():
    n,m = map(int,input().split())
    edge = []
    for i in range(m):
        edge.append(list(map(int,input().split())))
    minDist = [float('inf')]*(n+1)
    minDist[1] = 0

    for i in range(1,n):
        update = False
        for s,t,val in edge:
            if minDist[s] != float('inf') and minDist[s] + val < minDist[t]:
                minDist[t] = minDist[s] + val
                update = True
        if update == False:
            break
    if minDist[n] == float('inf'):
        return "unconnected"
    else:
        return minDist[n]
if __name__ == '__main__':
    print(main())
'''


import collections
def main():
    n,m = map(int,input().split())
    edge = [[] for i in range(n+1)] # 不能写成[[]*(n+1)] 这样写，生成的是一个空列表
    for i in range(m):
        s,t,val = map(int,input().split())
        edge[s].append([t,val])
    minDist= [float('inf')]*(n+1)
    visit = [False]*(n+1)
    que = collections.deque([1])
    minDist[1] = 0
    visit[1] = True
    while que:
        a = que.popleft()
        visit[a] = False
        for t,val in edge[a]:
            if minDist[a] != float('inf') and minDist[a]+val < minDist[t]:
                minDist[t] = minDist[a] + val
                if visit[t] == False:
                    visit[t] = True
                    que.append(t)
    if minDist[-1] == float('inf'):
        return 'unconnected'
    else:
        return minDist[-1]
if __name__ == '__main__':
    print(main())

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