Submission #27451237

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#ベルマンフォード負経路検出版
#参考（二つの内容を合わせた）
#https://qiita.com/kazukazukazukazu/items/e5db00a3aefb1f5ed72f
#https://sepat.hatenablog.com/entry/2019/08/15/223212
inf = float('inf')
class BellmanFord():
    def __init__(self, N):
        self.N = N
        self.edges = []
    def add(self, u, v, d, directed=False):
        """
        u = from, v = to, d = cost
        directed = Trueのとき、有向グラフである。
        """
        if directed is False:
            self.edges.append([u, v, d])
            self.edges.append([v, u, d])
        else:
            self.edges.append([u, v, d])
 
 
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#ベルマンフォード負経路検出版
#参考（二つの内容を合わせた）
#https://qiita.com/kazukazukazukazu/items/e5db00a3aefb1f5ed72f
#https://sepat.hatenablog.com/entry/2019/08/15/223212

inf = float('inf')
class BellmanFord():
    def __init__(self, N):
        self.N = N
        self.edges = []

    def add(self, u, v, d, directed=False):
        """
        u = from, v = to, d = cost
        directed = Trueのとき、有向グラフである。
        """
        if directed is False:
            self.edges.append([u, v, d])
            self.edges.append([v, u, d])
        else:
            self.edges.append([u, v, d])


    def BellmanFord_search(self, start):
        """
        :param s: 始点
        :return: d[i] 始点sから各点iまでの最短経路
        """
        #  infならたどり着けず
        # -infなら"通りたいパスに"負の閉路が存在する
        D = [inf for i in range(self.N)]
        D[start] = 0
        for i in range(self.N*2):
            for u,v,d in self.edges:
                if D[v] > D[u] + d:
                    D[v] = D[u] + d
                    #2巡目負経路が存在する場合の動き
                    if i>=self.N:
                        D[v]=-inf
        return D

N,M = map(int, input().split())
ABC = [list(map(int, input().split())) for _ in range(M)]
graph = BellmanFord(N)
for a,b,c in ABC:
    graph.add(a-1,b-1,-c,True)
d = graph.BellmanFord_search(0)
if d[N-1]==-inf:
    print('inf')
else:
    print(-d[N-1])

Submission Info

Judge Result