Problem p02679 (python)

Fixed submission:
import sys

readline = sys.stdin.readline
MOD = 10 ** 9 + 7
INF = float('INF')
sys.setrecursionlimit(10 ** 5)


def main():
    import fractions
    import math
    from collections import Counter
    n = int(readline())
    counter = Counter()
    a0, b0 = 0, 0
    lonely = 0

    for i in range(n):
        a, b = map(int, readline().split())
        if a == 0 and b == 0:
            lonely += 1
        elif a == 0:
            a0 += 1
        elif b == 0:
            b0 += 1
        else:
            fr = fractions.Fraction(a, b)
            counter[(fr.numerator, fr.denominator)] += 1

    ans = 1  # 最後に
    keys = list(counter.keys())
    for key in keys:
        nm1, dn1 = key[0], key[1]
        cnt1 = counter[(nm1, dn1)]
        nm2, dn2 = -(nm1 // abs(nm1)) * dn1, abs(nm1)
        cnt2 = counter[(nm2, dn2)]
        ans = ans * ((pow(2, cnt1, MOD) - 1) + (pow(2, cnt2, MOD) - 1) + 1)
        ans %= MOD
        counter[(nm1, dn1)] = 0
        counter[(nm2, dn2)] = 0

    ans *= ((pow(2, a0, MOD) - 1) + (pow(2, b0, MOD) - 1) + 1)
    ans %= MOD
    ans += lonely
    ans -= 1
    ans %= MOD

    print(ans)


if __name__ == '__main__':
    main()

Buggy submission (verdict: Runtime Error):
import sys

readline = sys.stdin.readline
MOD = 10 ** 9 + 7
INF = float('INF')
sys.setrecursionlimit(10 ** 5)


class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())


def main():
    n = int(input())
    mat = [list(map(int, readline().split())) for _ in range(n)]
    x = [a / b for a, b in mat]
    y = [-b / a for a, b in mat]

    from collections import Counter

    dislike = {i: [] for i in range(1, n + 1)}
    cx = Counter()
    cy = Counter()
    uf = UnionFind(n)

    for i, p in enumerate(x, 1):
        for j, q in enumerate(y, 1):
            if p == q:
                uf.union(i - 1, j - 1)
    sub = 0
    rem = n

    for val in uf.all_group_members().values():
        l = len(val)
        rem -= l
        if l >= 2:
            com = pow(2, l, MOD) - (l + 1)
            sub += (com * pow(2, rem, MOD) % MOD)

    ans = (pow(2, n, MOD) - 1 - sub) % MOD
    print(ans)


if __name__ == '__main__':
    main()