1118 birds in forest (25 分)

    Some scientists took pictures of thousands of birds in a forest. Assume that all the birds appear in the same picture belong to the same tree. You are supposed to help the scientists to count the maximum number of trees in the forest, and for any pair of birds, tell if they are on the same tree.

Input Specification:
Each input file contains one test case. For each case, the first line contains a positive number N (≤10^4) which is the number of pictures. Then N lines follow, each describes a picture in the format:
where K is the number of birds in this picture, and Bi 's are the indices of birds. It is guaranteed that the birds in all the pictures are numbered continuously from 1 to some number that is no more than 10^4.

After the pictures there is a positive number Q (≤10^4) which is the number of queries. Then Q lines follow, each contains the indices of two birds.

Output Specification:
For each test case, first output in a line the maximum possible number of trees and the number of birds. Then for each query, print in a line Yes if the two birds belong to the same tree, or No if not.

Sample Input:
4
3 10 1 2
2 3 4
4 1 5 7 8
3 9 6 4
2
10 5
3 7
Sample Output:
2 10
Yes
No

题意: 一些科学家拍摄了森林中成千上万只鸟的照片。假设所有鸟类出现在同一张图片中属于同一棵树。您应该帮助科学家计算森林中树木的最大数量，并且对于任何一对鸟类，都要知道它们是否在同一棵树上。

分析: 并查集

代码

using namespace std;


int n;
const int maxn = 10010;
vector<int> father(maxn);
int (int root)
{
    int son,tmp;
    son = root;
    while(father[root]!=root)
    {
        root=father[root];
    }
    return root;
}

void unio(int a,int b)
{
    int fa = find_father(a);
    int fb = find_father(b);
    if(fa!=fb)
        father[fa] = fb;
}

int main()
{
    while(scanf("%d",&n)!=EOF)
    {
        for(int i=0;i<maxn;i++)
            father[i]=i;
        int k,x,xb,maxx=0;
        for(int i=0;i<n;i++)
        {
            cin>>k>>x;
            maxx = max(x,maxx);
            for(int j=0;j<k-1;j++)
            {
                cin>>xb;
                maxx = max(maxx,xb);
                unio(x,xb);
            }
        }
        int cnt =0;
        for(int i=1;i<=maxx;i++)
            if(father[i]==i)
                cnt++;
        cout<<cnt<<" "<<maxx<<endl;
        int query;
        cin>>query;
        int a,b;
        for(int i=0;i<query;i++)
        {
            cin>>a>>b;
            if(find_father(a)==find_father(b))
                cout<<"Yes"<<endl;
            else
                cout<<"No"<<endl;
        }
    }
    return 0;
}