Problem: There are N persons called Person 1 through Person N.  You are given M facts that "Person A_i and Person B_i are friends." The same fact may be given multiple times.  If X and Y are friends, and Y and Z are friends, then X and Z are also friends. There is no friendship that cannot be derived from the M given facts.  Takahashi the evil wants to divide the N persons into some number of groups so that every person has no friend in his/her group.  At least how many groups does he need to make?

Submission attempts (in order):
import collections


class unionFind:
    parent = []

    def __init__(self, N):
        self.parent = [i for i in range(N)]

    def root(self, x):
        if self.parent[x] == x:
            return(x)
        else:
            self.parent[x] = self.root(self.parent[x])
            return(self.parent[x])

    def same(self, x, y):
        x, y = x-1, y-1
        return(self.root(x) == self.root(y))

    def unite(self, x, y):
        x, y = x-1, y-1
        x = self.root(x)
        y = self.root(y)
        if x == y:
            return
        else:
            self.parent[x] = y
            return


N, M = map(int, input().split())
G = unionFind(N)
for i in range(M):
    a, b = map(int, input().split())
    G.unite(a, b)

for i in range(N):
    G.root(i)

C = collections.Counter(G.parent).most_common()

print(1)
# print(C[0][1])


import collections


class unionFind:
    parent = []

    def __init__(self, N):
        self.parent = [i for i in range(N)]

    def root(self, x):
        if self.parent[x] == x:
            return(x)
        else:
            self.parent[x] = self.root(self.parent[x])
            return(self.parent[x])

    def same(self, x, y):
        x, y = x-1, y-1
        return(self.root(x) == self.root(y))

    def unite(self, x, y):
        x, y = x-1, y-1
        x = self.root(x)
        y = self.root(y)
        if x == y:
            return
        else:
            self.parent[x] = y
            return


N, M = map(int, input().split())
G = unionFind(N)
for i in range(M):
    a, b = map(int, input().split())
    G.unite(a, b)
print(1)


#     G.root(i)

# C = collections.Counter(G.parent).most_common()

# print(C[0][1])


import collections


class unionFind:
    parent = []

    def __init__(self, N):
        self.parent = [i for i in range(N)]

    def root(self, x):
        if self.parent[x] == x:
            return(x)
        else:
            self.parent[x] = self.root(self.parent[x])
            return(self.parent[x])

    def same(self, x, y):
        x, y = x-1, y-1
        return(self.root(x) == self.root(y))

    def unite(self, x, y):
        x, y = x-1, y-1
        x = self.root(x)
        y = self.root(y)
        if x == y:
            return
        else:
            self.parent[x] = y
            return


N, M = map(int, input().split())
G = unionFind(N)
for i in range(M):
    a, b = map(int, input().split())
    G.unite(a, b)

for i in range(N):
    G.root(i)
print(1)
# C = collections.Counter(G.parent).most_common()

# print(C[0][1])


import collections
import sys
sys.setrecursionlimit(10**6)
N, M = map(int, input().split())
AB = [tuple(map(int, input().split())) for i in range(M)]


class unionFind:
    parent = []

    def __init__(self, N):
        self.parent = [i for i in range(N)]

    def root(self, x):
        if self.parent[x] == x:
            return(x)
        else:
            self.parent[x] = self.root(self.parent[x])
            return(self.parent[x])

    def same(self, x, y):
        x, y = x-1, y-1
        return(self.root(x) == self.root(y))

    def unite(self, x, y):
        x, y = x-1, y-1
        x = self.root(x)
        y = self.root(y)
        if x == y:
            return
        else:
            self.parent[x] = y
            return


G = unionFind(N)

for a, b in AB:
    G.unite(a, b)

for i in range(N):
    G.root(i)

C = collections.Counter(G.parent).most_common()

print(C[0][1])


Verdicts: Runtime Error

Wrong Answer

Runtime Error

Accepted