Bellman_ford算法

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())

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