Problem p02762 (python)

Fixed submission:
from collections import defaultdict


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())


if __name__ == '__main__':
    n, m, k = list(map(int, input().split()))
    friends = UnionFind(n)
    ng_dict = defaultdict(list)

    for i in range(m):
        data = list(map(int, input().split()))
        x = data[0] - 1
        y = data[1] - 1

        friends.union(x, y)
        ng_dict[x].append(y)
        ng_dict[y].append(x)

    for i in range(k):
        data = list(map(int, input().split()))
        x = data[0] - 1
        y = data[1] - 1

        if friends.same(x, y):
            ng_dict[x].append(y)
            ng_dict[y].append(x)

    for i in range(n):
        print(friends.size(i) - len(ng_dict[i]) - 1, end=" ")

Buggy submission (verdict: Runtime Error):
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())


if __name__ == '__main__':
    n, m, k = list(map(int, input().split()))
    friends = UnionFind(n)
    ng_dict = {}
    for i in range(m):
        data = list(map(int, input().split()))
        friends.union(data[0] - 1, data[1] - 1)
        if (data[0] - 1) in ng_dict:
            ng_dict[data[0] - 1].append(data[1] - 1)
        else:
            ng_dict[data[0] - 1] = [(data[1] - 1)]
        if (data[1] - 1) in ng_dict:
            ng_dict[data[1] - 1].append(data[0] - 1)
        else:
            ng_dict[data[1] - 1] = [(data[0] - 1)]

    for i in range(k):
        data = list(map(int, input().split()))
        if friends.same(data[0] - 1, data[1] - 1):
            if (data[0] - 1) in ng_dict:
                ng_dict[data[0] - 1].append(data[1] - 1)
            else:
                ng_dict[data[0] - 1] = [(data[1] - 1)]
            if (data[1] - 1) in ng_dict:
                ng_dict[data[1] - 1].append(data[0] - 1)
            else:
                ng_dict[data[1] - 1] = [(data[0] - 1)]

    for i in range(n):
        print(friends.size(i) - len(ng_dict[i]) - 1, end=" ")