Problem p02573 (python)

Fixed submission:
class UnionFind:
    def __init__(self, N):
        self.parent = list(range(N))
        self.rank = [0] * N
        self.size = [1] * N

    def find(self, x):
        r = x
        while self.parent[r] != r:
            r = self.parent[r]
        while self.parent[x] != r:
            x, self.parent[x] = self.parent[x], r
        return r

    def unite(self, x, y):
        x = self.find(x)
        y = self.find(y)
        if x == y:
            return
        if self.rank[x] < self.rank[y]:
            self.parent[x] = y
            self.size[y] += self.size[x]
        else:
            self.parent[y] = x
            self.size[x] += self.size[y]
            if self.rank[x] == self.rank[y]:
                self.rank[x] += 1

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

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

N, M = map(int, input().split())
uf = UnionFind(N)
for _ in range(M):
    A, B = map(int, input().split())
    uf.unite(A-1, B-1)

ans = max(uf.get_size(i) for i in range(N))
print(ans)

Buggy submission (verdict: Runtime Error):
N, M = map(int, input().split())

members = [-1] * N

group_count = 0
groups = [0] * N
group_dict = {}
for m in range(M):
    A, B = map(int, input().split())
    A = A - 1
    B = B - 1
    if members[A]==-1 and members[B]==-1:
        members[A] = members[B] = group_count
        groups[group_count] = 2
        group_dict[group_count] = [A, B]
        group_count += 1
    
    elif members[A]!=-1 and members[B]==-1:
        members[B] = members[A]
        groups[members[A]] += 1
        group_dict[members[A]].append(B)
    
    elif members[B]!=-1 and members[A]==-1:
        members[A] = members[B]
        groups[members[B]] += 1
        group_dict[members[B]].append(A)
    
    else:
        if members[A] != members[B]:
            if len(group_dict[A]) > len(group_dict[B]):
                old = members[B]
                groups[members[A]] += groups[members[B]]
                groups[members[B]] = 0
                group_dict[members[A]] = group_dict[members[A]] +  group_dict[members[B]]
                for aaaaaa in group_dict[members[B]]:
                    members[aaaaaa] = members[A]
                group_dict[old] = []
            else:
                old = members[A]
                groups[members[B]] += groups[members[B]]
                groups[members[A]] = 0
                group_dict[members[B]] = group_dict[members[B]] + group_dict[members[A]]
                for bbbbbb in group_dict[members[A]]:
                    members[bbbbbb] = members[B]
                group_dict[old] = []

ans = max(groups)
if ans == 0:
    print(1)
else:
    print(ans)

Buggy submission (verdict: Runtime Error):
import numpy as np

N, M = map(int, input().split())

members = np.array([-1] * N).astype(np.int)

group_count = 0
groups = [0] * N
group_dict = {}
for m in range(M):
    A, B = map(int, input().split())
    A = A - 1
    B = B - 1
    if members[A]==-1 and members[B]==-1:
        members[A] = members[B] = group_count
        groups[group_count] = 2
        group_dict[group_count] = [A, B]
        group_count += 1
    
    elif members[A]!=-1 and members[B]==-1:
        members[B] = members[A]
        groups[members[A]] += 1
        group_dict[members[A]].append(B)
    
    elif members[B]!=-1 and members[A]==-1:
        members[A] = members[B]
        groups[members[B]] += 1
        group_dict[members[B]].append(A)
    
    else:
        if members[A] != members[B]:
            old = members[B]
            groups[members[A]] += groups[members[B]]
            groups[members[B]] = 0
            group_dict[members[A]] = group_dict[members[A]] +  group_dict[members[B]]
            for aaaaaa in group_dict[members[B]]:
                members[aaaaaa] = members[A]
            group_dict[old] = []

ans = max(groups)
if ans == 0:
    print(1)
else:
    print(ans)