Submission #37340898

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Source Code Expand

from bisect import bisect_left


def main():
    global N, M, edges
    N, M = map(int, input().split())
    edges = [tuple(map(lambda x: int(x)-1, input().split())) for _ in range(M)]

    ans = solve()
    print(ans)


def solve():
    dsu = DSU(2*N)

    for u, v in edges:
        dsu.merge(u, v+N)
        dsu.merge(u+N, v)

    for i in range(N):
        if dsu.same(i, i+N): return 0

    ret = N*(N-1)//2 - M
    for g in dsu.groups():
        cnt = bisect_left(g, N)
        ret -= cnt*(cnt-1)//2

    return ret


class DSU:
    def __init__(self, n):
        self._n = n
        self.parent_or_size = [-1] * n

    def merge(self, a, b):
        assert 0 <= a < self._n
        assert 0 <= b < self._n
        x, y = self.leader(a), self.leader(b)
        if x == y: return x
        if -self.parent_or_size[x] < -self.parent_or_size[y]: x, y = y, x
        self.parent_or_size[x] += self.parent_or_size[y]
        self.parent_or_size[y] = x
        return x

    def same(self, a, b):
        assert 0 <= a < self._n
        assert 0 <= b < self._n
        return self.leader(a) == self.leader(b)

    def leader(self, a):
        assert 0 <= a < self._n
        if self.parent_or_size[a] < 0: return a
        self.parent_or_size[a] = self.leader(self.parent_or_size[a])
        return self.parent_or_size[a]

    def size(self, a):
        assert 0 <= a < self._n
        return -self.parent_or_size[self.leader(a)]

    def groups(self):
        leader_buf = [self.leader(i) for i in range(self._n)]
        result = [[] for _ in range(self._n)]
        for i in range(self._n): result[leader_buf[i]].append(i)
        return [r for r in result if r != []]


if __name__ == '__main__': main()

Submission Info

Judge Result