pku 1611 The Suspects 并查集的应用

http://poj.org/problem?id=1611

思路：统计出和0能够联系在一起的点，然后输出其个数

#include <cstdio>
#include <iostream>
#define maxn 30004
using namespace std;

int f[maxn],num[maxn];//num记录与0有联系的个数
int n,m;

int find(int x)
{
if (x != f[x])
    {
        f[x] = find(f[x]);
    }
return f[x];
}
void Union(int x,int y)
{
    x = find(x);
    y = find(y);
if (x != y)
    {
        f[y] = x;
        num[x] += num[y];//根记录子系的个数
    }
}
int main()
{
int i,j,a,b,k;
while (cin>>n>>m)
    {
if (!n && !m) break;
for (i = 0; i <= n; ++i)
        {
            f[i] = i;
            num[i] = 1;
        }
for (i = 0; i < m; ++i)
        {
            cin>>k;
if (k)
            cin>>a;
for (j = 1; j < k; ++j)
            {

                cin>>b;
                Union(a,b);
            }
        }
int pos = find(0);//找到0所在的子系的根
        printf("%d\n",num[pos]);

    }
return 0;
}