Buggy python submission (verdict: Time Limit Exceeded):
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())



f=lambda:map(int,input().split())
N,M=f()
uf=UnionFind(N+1)
for _ in range(M):
    a,b=f()
    uf.union(a,b)
    
print(max([len(i) for i in list(uf.all_group_members().values())]))

Fixed submission:
# D
from collections import deque
from bisect import bisect_left as bl

f=lambda:map(int,input().split())
N,M=f()
D=[[] for _ in [0]*(N+1)]
F=[0]*(N+1)
F[0]=1
for _ in range(M):
    a,b=f()
    D[a].append(b)
    D[b].append(a)

q=deque()
res=0


while bl(F,1):
    index=bl(F,1)-1
    q.append(index)
    tmp=0
    while q:
        k=q.pop()
        if F[k]!=1:
            tmp+=1
            F[k]=1
            for d in list(set(D[k])):
                if F[d]!=1:
                    q.append(d)
            D[k]=0
    res=max(res,tmp)

print(res)

Buggy python submission (verdict: Time Limit Exceeded):
# D
from collections import deque
from bisect import bisect_left as bl

f=lambda:map(int,input().split())
N,M=f()
D=[[] for _ in [0]*(N+1)]
F=[0]*(N+1)
F[0]=1
for _ in range(M):
    a,b=f()
    if not b in D[a]:
        D[a].append(b)
    if not a in D[b]:
        D[b].append(a)

q=deque()
res=0
while bl(F,1):
    index=bl(F,1)-1
    q.append(index)
    tmp=0
    while q:
        k=q.pop()
        if F[k]!=1:
            tmp+=1
            F[k]=1
            for d in D[k]:
                if F[d]!=1:
                    q.append(d)
            D[k]=0
    res=max(res,tmp)

print(res)

Fixed submission:
# D
from collections import deque
from bisect import bisect_left as bl

f=lambda:map(int,input().split())
N,M=f()
D=[[] for _ in [0]*(N+1)]
F=[0]*(N+1)
F[0]=1
for _ in range(M):
    a,b=f()
    D[a].append(b)
    D[b].append(a)

q=deque()
res=0


while bl(F,1):
    index=bl(F,1)-1
    q.append(index)
    tmp=0
    while q:
        k=q.pop()
        if F[k]!=1:
            tmp+=1
            F[k]=1
            for d in list(set(D[k])):
                if F[d]!=1:
                    q.append(d)
            D[k]=0
    res=max(res,tmp)

print(res)

Buggy python submission (verdict: Time Limit Exceeded):
# D
from collections import deque
from bisect import bisect_left as bl

f=lambda:map(int,input().split())
N,M=f()
D=[[] for _ in [0]*(N+1)]
F=[0]*(N+1)
F[0]=1
for _ in range(M):
    a,b=f()
    if not b in D[a]:
        D[a].append(b)
    if not a in D[b]:
        D[b].append(a)

q=deque()
res=0
while bl(F,1):
    index=bl(F,1)-1
    q.appendleft(index)
    tmp=0
    while q:
        k=q.pop()
        if F[k]!=1:
            tmp+=1
            q.extend(D[k])
            D[k]=0
            F[k]=1
    res=max(res,tmp)

print(res)

Fixed submission:
# D
from collections import deque
from bisect import bisect_left as bl

f=lambda:map(int,input().split())
N,M=f()
D=[[] for _ in [0]*(N+1)]
F=[0]*(N+1)
F[0]=1
for _ in range(M):
    a,b=f()
    D[a].append(b)
    D[b].append(a)

q=deque()
res=0


while bl(F,1):
    index=bl(F,1)-1
    q.append(index)
    tmp=0
    while q:
        k=q.pop()
        if F[k]!=1:
            tmp+=1
            F[k]=1
            for d in list(set(D[k])):
                if F[d]!=1:
                    q.append(d)
            D[k]=0
    res=max(res,tmp)

print(res)

Buggy python submission (verdict: Time Limit Exceeded):
# D
from collections import deque
from bisect import bisect_left as bl

f=lambda:map(int,input().split())
N,M=f()
D=[[] for _ in [0]*(N+1)]
F=[0]*(N+1)
F[0]=1
for _ in range(M):
    a,b=f()
    if not b in D[a]:
        D[a].append(b)
    if not a in D[b]:
        D[b].append(a)

q=deque()
res=0
while bl(F,1):
    index=bl(F,1)-1
    q.appendleft(index)
    tmp=0
    while q:
        k=q.pop()
        if F[k]!=1:
            tmp+=1
            q.extend(D[k])
            D[k]=0
            F[k]=1
    res=max(res,tmp)

print(res)

Fixed submission:
# D
from collections import deque
from bisect import bisect_left as bl

f=lambda:map(int,input().split())
N,M=f()
D=[[] for _ in [0]*(N+1)]
F=[0]*(N+1)
F[0]=1
for _ in range(M):
    a,b=f()
    D[a].append(b)
    D[b].append(a)

q=deque()
res=0


while bl(F,1):
    index=bl(F,1)-1
    q.append(index)
    tmp=0
    while q:
        k=q.pop()
        if F[k]!=1:
            tmp+=1
            F[k]=1
            for d in list(set(D[k])):
                if F[d]!=1:
                    q.append(d)
            D[k]=0
    res=max(res,tmp)

print(res)

Buggy python submission (verdict: Time Limit Exceeded):
# D
from collections import deque
from bisect import bisect_left as bl

f=lambda:map(int,input().split())
N,M=f()
D=[[] for _ in [0]*(N+1)]
F=[0]*(N+1)
F[0]=1
for _ in range(M):
    a,b=f()
    if not b in D[a]:
        D[a].append(b)
    if not a in D[b]:
        D[b].append(a)

q=deque()
res=[]
while bl(F,1):
    index=bl(F,1)-1
    q.append(index)
    tmp=0
    while q:
        k=q.pop()
        if F[k]!=1:
            tmp+=1
            q.extend(D[k])
            D[k]=0
            F[k]=1
    res.append(tmp)

print(max(res))

Fixed submission:
# D
from collections import deque
from bisect import bisect_left as bl

f=lambda:map(int,input().split())
N,M=f()
D=[[] for _ in [0]*(N+1)]
F=[0]*(N+1)
F[0]=1
for _ in range(M):
    a,b=f()
    D[a].append(b)
    D[b].append(a)

q=deque()
res=0


while bl(F,1):
    index=bl(F,1)-1
    q.append(index)
    tmp=0
    while q:
        k=q.pop()
        if F[k]!=1:
            tmp+=1
            F[k]=1
            for d in list(set(D[k])):
                if F[d]!=1:
                    q.append(d)
            D[k]=0
    res=max(res,tmp)

print(res)