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):
#!/usr/bin/env python3
def main():
    from collections import deque

    N, M = map(int, input().split())
    friends_input = [set() for _ in range(N)]
    for _ in range(M):
        a, b = map(int, input().split())
        friends_input[a - 1].add(b - 1)
        friends_input[b - 1].add(a - 1)

    seen = [False] * N
    friends_group = []
    for i in range(N):
        if seen[i]:
            continue
        q = deque([i])
        tmp_group = [i]
        while q:
            now = q.popleft()
            if seen[now]:
                continue
            seen[now] = True
            for j in friends_input[now]:
                if not seen[j]:
                    q.append(j)
                    tmp_group.append(j)
        friends_group.append(tmp_group)
    ans = 0
    for i in friends_group:
        ans = max(ans, len(i))
    print(ans)
    print(friends_group)


if __name__ == '__main__':
    main()


#!/usr/bin/env python3
class unionfind:
    """Union-Find"""
    def __init__(self, n: int):
        """
        Constructer(Initialize parameter in this class)

        Parameters
        ----------
        n : int
            Number of node
        
        Yields
        -----
        root : list
            When value is postive, express root of the node.
            When it is negative, express this node is root and size of set.
        """

        self.root = [-1] * n

    def find(self, x: int):
        """
        Search root of node x

        Parameters
        ----------
        x : int
            node x

        Returns
        -------
        x : int
            Root of node x
        """

        if self.root[x] < 0:
            return x
        self.root[x] = self.find(self.root[x])
        return self.root[x]
    
    def unite(self, x: int, y: int):
        """
        Unite two set including node x and node y into one set.

        Parameters
        ----------
        x, y : int
            Node number

        Returns
        -------
        unite_result : bool
            False : Already two node include same set.
            True  : United
        """

        x = self.find(x)
        y = self.find(y)
        if x == y:
            return False
        if self.root[x] > self.root[y]:
            x, y = y, x
        self.root[x] += self.root[y]
        self.root[y] = x
        return True

    def same(self, x: int, y: int):
        """
        Determine if x and y are in same set.

        Parameters
        ----------
        x, y : int
            Node number

        Returns
        -------
        result : bool
            Determining result
        """

        return self.find(x) == self.find(y)
    
    def size(self, x: int) -> bool:
        """
        Return size of set including node x.

        Parameters
        ----------
        x : int
            Node number

        Returns
        -------
        Size of set : int
        """

        return self.root[self.find(x)] * -1


def main():
    N, M = map(int, input().split())
    uf = unionfind(N)
    for _ in range(M):
        a, b = map(int, input().split())
        a -= 1
        b -= 1
        uf.unite(a, b)

    ans = 0
    for i in range(N):
        ans = max(ans, uf.size(i))
    print(ans)


if __name__ == '__main__':
    main()


Verdicts: Wrong Answer

Accepted