C :

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int f[30010], weight[30010];

int find(int v){
if(v == f[v])return v;
int F = find(f[v]);
f[v] = F;
return F;
}

int main()
{
    int n, m;
    while(scanf("%d%d",&n,&m) != EOF){
        for(int i = 0;i <= n; i++)f[i] = i;
        memset(weight,0,sizeof(weight));
        while(m--){
            int k,first;
            scanf("%d%d",&k,&first);
            int fa = find(first);
            while(--k){
                int b;
                scanf("%d",&b);
                int fb = find(b);
                f[fb] = fa;
            }
        }
        int max = 0;
        for(int i = 1;i <= n; i++){
            int fa = find(i);
            weight[fa]++;
        }
        for(int i = 1;i <= n; i++){
            if(max < weight[i])max = weight[i];
        }
        printf("%d\n",max);
    }

    return 0;
}

C++ :

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;

const int maxn=30010;

int pre[maxn],a[maxn],h[maxn];

int find(int x)
{
    int r=x;
    while(r!=pre[r]) r=pre[r];
    int temp;
    while(x!=r)
    {
        temp=pre[x];
        pre[x]=r;
        x=temp;
    }
    return r;
}

void join(int x,int y)
{
    int fx=find(x);
    int fy=find(y);
    if(fx!=fy) pre[fx]=fy;
}

int main()
{
    int n,m;
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        for(int i=1;i<=n;i++) pre[i]=i;
        memset(h,0,sizeof(h));
        int num;
        for(int i=0;i<m;i++)
        {
            scanf("%d",&num);
            for(int j=0;j<num;j++) scanf("%d",&a[j]);
            for(int j=1;j<num;j++) join(a[0],a[j]);
        }
        for(int i=1;i<=n;i++) h[find(i)]++;
        int k=1;
        for(int i=2;i<=n;i++)
        {
            if(h[i]>h[k]) k=i;
        }
        printf("%d\n",h[k]);
    }
}