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())

def main():
  n, m = map(int, input().split())
  uf = UnionFind(n)

  for i in range(m):
    a, b = map(int, input().split())
    a -= 1; b-= 1;
    uf.union(a, b)
  
  max_len = 0
  for g in list(uf.all_group_members().values()):
    len_g = len(g)
    if len_g > max_len:
      max_len = len_g
      
  print(max_len)
  
main()

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

def main():
  n, m = map(int, input().split())
  uf = UnionFind(n)

  for i in range(m):
    a, b = map(int, input().split())
    a -= 1; b-= 1;
    uf.union(a, b)
  
  ans = 0
  for i in range(n):
    ans = max(ans, uf.size(i))
      
  print(ans)
  
main()

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque

def main():
  n, m = map(int, input().split())
  graph = [[] for _ in range(n)]

  for i in range(m):
    a, b = map(int, input().split())
    if b-1 not in graph[a-1]:
      graph[a-1].append(b-1)
      graph[b-1].append(a-1)
  
  unsearched = list(range(n))
  result = 0
  border = n//2
  while len(unsearched) > 0:
    if result > border:
      break
    s = unsearched[0]
    tmp, cnt = dfs(graph, unsearched, s)
    if cnt > result:
      result = cnt
      
  print(result)

def dfs(graph, unsearched, s):
  stack = deque([s])
  searched = [s]
  while len(stack):
    cur = stack.pop()
    unsearched.remove(cur)
    for i in graph[cur]:
      if i not in searched:
        stack.append(i)
        searched += [i]
  return searched, len(searched)

main()

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

def main():
  n, m = map(int, input().split())
  uf = UnionFind(n)

  for i in range(m):
    a, b = map(int, input().split())
    a -= 1; b-= 1;
    uf.union(a, b)
  
  ans = 0
  for i in range(n):
    ans = max(ans, uf.size(i))
      
  print(ans)
  
main()

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque

def main():
  n, m = map(int, input().split())
  graph = [[] for _ in range(n)]

  for i in range(m):
    a, b = map(int, input().split())
    if b-1 not in graph[a-1]:
      graph[a-1].append(b-1)
      graph[b-1].append(a-1)
  
  unsearched = list(range(n))
  result = 0
  border = n//2
  while len(unsearched) > 0:
    s = unsearched[0]
    tmp, cnt = dfs(graph, unsearched, s)
    if cnt > result:
      result = cnt
      
  print(result)

def dfs(graph, unsearched, s):
  stack = deque([s])
  searched = [s]
  while len(stack):
    cur = stack.pop()
    unsearched.remove(cur)
    for i in graph[cur]:
      if i not in searched:
        stack.append(i)
        searched += [i]
  return searched, len(searched)

main()

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

def main():
  n, m = map(int, input().split())
  uf = UnionFind(n)

  for i in range(m):
    a, b = map(int, input().split())
    a -= 1; b-= 1;
    uf.union(a, b)
  
  ans = 0
  for i in range(n):
    ans = max(ans, uf.size(i))
      
  print(ans)
  
main()

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque

def main():
  n, m = map(int, input().split())
  graph = [[] for _ in range(n)]

  for i in range(m):
    a, b = map(int, input().split())
    if b-1 not in graph[a-1]:
      graph[a-1].append(b-1)
      graph[b-1].append(a-1)
  
  searched = []
  result = 0
  while len(searched) != n:
    for i in range(n):
      if i not in searched:
        s = i
        break
    tmp, cnt = dfs(graph, s)
    searched += tmp
    if cnt > result:
      result = cnt
      
  print(result)

def dfs(graph, s):
  stack = deque([s])
  searched = [s]
  while len(stack):
    cur = stack.pop()
    for i in graph[cur]:
      if i not in searched:
        stack.append(i)
        searched += [i]
  return searched, len(searched)

main()

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

def main():
  n, m = map(int, input().split())
  uf = UnionFind(n)

  for i in range(m):
    a, b = map(int, input().split())
    a -= 1; b-= 1;
    uf.union(a, b)
  
  ans = 0
  for i in range(n):
    ans = max(ans, uf.size(i))
      
  print(ans)
  
main()