Submission #7103803

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Source Code Expand

# Dinic's algorithm
from collections import deque
class Dinic:
    def __init__(self, N):
        self.N = N
        self.G = [[] for i in range(N)]

    def add_edge(self, fr, to, cap):
        forward = [to, cap, None]
        forward[2] = backward = [fr, 0, forward]
        self.G[fr].append(forward)
        self.G[to].append(backward)

    def add_multi_edge(self, v1, v2, cap1, cap2):
        edge1 = [v2, cap1, None]
        edge1[2] = edge2 = [v1, cap2, edge1]
        self.G[v1].append(edge1)
        self.G[v2].append(edge2)

    def bfs(self, s, t):
        self.level = level = [None]*self.N
        deq = deque([s])
        level[s] = 0
        G = self.G
        while deq:
            v = deq.popleft()
            lv = level[v] + 1
            for w, cap, _ in G[v]:
                if cap and level[w] is None:
                    level[w] = lv
                    deq.append(w)
        return level[t] is not None

    def dfs(self, v, t, f):
        if v == t:
            return f
        level = self.level
        for e in self.it[v]:
            w, cap, rev = e
            if cap and level[v] < level[w]:
                d = self.dfs(w, t, min(f, cap))
                if d:
                    e[1] -= d
                    rev[1] += d
                    return d
        return 0

    def flow(self, s, t):
        flow = 0
        INF = 10**18
        G = self.G
        while self.bfs(s, t):
            *self.it, = map(iter, self.G)
            f = INF
            while f:
                f = self.dfs(s, t, INF)
                flow += f
        return flow

N, M = map(int, input().split())
din = Dinic(2*N+2) #2N = t, 2N+1 = s
inf = 10 ** 18

c = list(map(int, input().split()))
for i in range(N):
    if i == 0:
        din.add_edge(0, 1, 0)
    elif i == N-1:
        din.add_edge(2*(N-1), 2*(N-1)+1, 0)
    else:
        cost = c[i-1]
        if cost == -1:
            din.add_edge(2*i, 2*N, inf)
            din.add_edge(2*N+1, 2*i+1, inf)
        else:
            din.add_edge(2*i, 2*i+1, cost)

for i in range(M):
    a, b = map(int, input().split())
    a -= 1
    b -= 1
    din.add_edge(2*a+1, 2*b, inf)
    
ans = din.flow(2*N+1, 2*N)
if ans >= inf:
    print(-1)
else:
    print(ans)

Submission Info

Judge Result